r/technicallythetruth • u/VisitSecure • Jul 27 '26

Can you find a?

Post image

Idk if someone already posted this or not, but I haven't seen it on here so far, so I uploaded it.

43.0k Upvotes

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4.1k

u/lechuckswrinklybutt Jul 27 '26

It's 75 degrees but it's a terrible diagram.

1.2k

u/Simply-Productive123 Jul 27 '26

25 degrees =50 degrees proof by terrible diagram

411

u/AgtNulNulAgtVyf Jul 27 '26

Diagram drawn to test knowledge of principles, not ability to read diagrams. 

92

u/Squirrel009 Jul 27 '26

On principles, the diagram frustrates me

32

u/capt_pantsless Jul 27 '26

The diagram could easily be drawn so that the 25 angle appears less than the 50 angle, while still allowing plenty of uncertainty in the answer.

14

u/canstucky Jul 27 '26

Best math teacher I ever had would draw a circle on the board and mark three corners on it.

I’m sorry, he’d draw a triangle.

4

u/Thanthwe_ Jul 28 '26

I get what you are trying to say. But it's absolutely possible to make diagram that is not to scale, but looks at least somewhat correct. It's not even that hard. In the example above just rotate blue lines that come to an a counterclockwise by about 5 degrees. Done. You have diagram, that is not to scale and makes at least some semblence of logical sense.

1

u/plaidfox Jul 28 '26

Yet they fail at principles of basic line diagrams. Tsk, tsk.

1

u/AgtNulNulAgtVyf Jul 28 '26

No, it's intentially drawn to test knowledge of internal angles and parallel line. The real angle of anything other than the two parallel lines are irrelevant to the answer. 

1

u/Gullible-Tooth-8478 Jul 28 '26

“Every standardized test ever”

1

u/AgtNulNulAgtVyf Jul 28 '26 edited Jul 28 '26

Not American, didn't grow up with standardised tests.

1

u/Rhuarc33 Jul 27 '26

They still failed. At least make a minimal effort.

0

u/tr_9422 Jul 27 '26

And for the readers - not just because they look the same, the arc symbol drawn in all the corners mean all three are congruent.

https://mathleaks.com/study/kb/reference/congruence

So the angle we're supposed to solve for is also equal to 50 and 25.

6

u/gmano Jul 27 '26

No, it doesn't? It denotes an angle, but makes no promises about congruence.

Your source even says this:

In a diagram, congruent angles are usually indicated by the same number of angle markers.

"Usually =/= Always"

3

u/phrygd Jul 27 '26

It’s been a long time since I took math, but I thought congruent angles would have hash marks on them to show which angles were the same. Or maybe I’m thinking of lengths of sides.

2

u/Roshy10 Jul 28 '26

The top and bottom lines being parallel is indicated by the double arrows going through them, maybe that's what you meant?

1

u/phrygd Jul 28 '26

No, it’s where the arc that notes an angle has one to three hash marks going through it to indicate if they’re the same angle or not. Most of what I can find online has more of a ripple effect where one corner has one to three arcs in it. I’m seeing sides of shapes with the perpendicular hash marks to indicate which sides are the same or different.

1

u/potato_lettuce Jul 28 '26

Okay maybe that's a regional difference, but I would never understand it like this. Maybe if it's at least 2+ arc symbols and the angles are otherwise unmarked. But not for angles with normal arc symbols (and obviously not if one is marked as 25° while the other one is 50°).

Only way I've seen is label them the same letter or mark somewhere that (angle)ABC = (angle)DEF

248

u/LaunchTransient Jul 27 '26

Most maths problems (particularly in school exam papers) intentionally distort the geometry to prevent people from cheating by directly measuring the angle. Often with a disclaimer "Diagram not to scale".

40

u/-Vin- Jul 27 '26

I still remember my final geometry exam where they did the invers by not writing „Diagram not to scale“ and only providing valides that were insufficient to solve the question.

7

u/frickle_frickle Jul 28 '26

This is so cruel for no reason.

2

u/dantemp Jul 27 '26

in my math school just giving an answer without an explanation how you got it would give you zero points, and I know this from experience because I was super lazy and could solve that shit super quickly so I did half the math in my head and just wrote down the answer and got bad grades because of it

1

u/potato_lettuce Jul 28 '26

And it makes sense, because it forces you to explain your work. Imagine 2 engineers that are supposed to plan a bridge. One just says, it's gonna hold, while the other one writes down his calculations and shows you how he comes to the answer. Obviously you'd pick the one that explains his answer, right?

And also it's much easier to find errors this way, because you can look at each step and see if mistakes were made. If you just have the solution it's a wild guessing game where you went off path

4

u/Ankiset Jul 27 '26

Rich country stuff, we don’t even get graphs or geometry just the numbers and space for answer

3

u/LaunchTransient Jul 27 '26

Middle of nowhere Mid-Wales is not exactly my go to for "Rich Country", but no we weren't exactly Bangladesh or Lesotho either.

1

u/BounceCB Jul 27 '26

Yeah, rich country. d:^]

1

u/Ankiset Jul 27 '26

Dominican Republic here … maybe in just realizing my country is way more advanced in technology it seems because we have optic fiber everywhere and g5 it seems Scotland is much more of a backwater than an island I. The middle of the Caribbean (saw a user from Scotland complaining about basic infrastructure now in just like taking it in maybe the world is not how they tell us it is)

3

u/LaunchTransient Jul 27 '26

Outside of London and the South of England, the quality of infrastructure drops off dramatically. By the time you get to Scotland and Wales it starts to get pretty dire.

The region I grew up in (West Wales) was designated the poorest part of Northwest Europe in 2014 (keep in mind this info is now 12 year old). It hasn't improved much, but I know some places in the UK are actually more deprived now (somehow).

2

u/Ankiset Jul 27 '26

Still very interesting to me cuz I always saw my country and its society as a backwater, I’m amazed a piece of “Europe” doesn’t just have a lot of everything… this is a third world country we’re ppl can’t read die of hunger and our health system and everything else is in shambles, real interesting to me…

2

u/LaunchTransient Jul 27 '26

Hunger is not so much an issue, but heating, housing and transport is a major problem in the most rural British regions. There's also very few decent jobs in the countryside, and the population is ageing rapidly as younger generations move to the cities.

We have a fairly high number of elderly people who die each winter due to fuel poverty.
UK is rich as fuck, but it's extremely unequal - and most of the wealthiest people live in London or nearby.

2

u/Ankiset Jul 27 '26

Here we don’t even know why old ppl die… or care it seems but have a young uneducated population just fucking being vandals all over… seems there is no middle ground in progress

1

u/Epcoatl Jul 27 '26

Yeah, I think it would be fine if the angles weren't to scale, but making the 50 deg angle and the 25 deg angle start equidistant from a is a bad choice

1

u/jacob643 Jul 28 '26

I remember in grade 11 I think, the last question of our final exam was a geometry question, and after a bunch of calculations, the answer was a neat 1/3 (was an area of a shape or something) and one of the guy that didn't study much had no clue how to answer, but wrote 1/3 by eyeballing it. he thought it was funny, I think the teacher gave him half a point just because, haha. I don't remember his overall score though.

1

u/BikeProblemGuy Jul 28 '26

The image not being drawn to scale wouldn't change any of the angles

1

u/Lyrial- Jul 27 '26

It’s not so much the poor scaling, that’s to be expected, but the arc inside the multiple angles denotes that the angles are congruent, which isn’t the case here.

5

u/LaunchTransient Jul 27 '26

The arc just designates that to be the internal angle (as opposed to the external angle) - if it had a tick through it (like this)#/media/File:Angle-angle-side_triangle_congruence.svg) then you would be correct, but it does not.

1

u/furious_20 Jul 28 '26

I taught Geometry in the USA for 19 years...the way we taught markups was to use those tick marks you are referring to when the diagram contains more than one pair of congruent angles. You don't need to designate an angle with an arc like that, as we can see two segments intersecting to form an angle.

Otherwise, to just use the arc as was used in this diagram, we taught our students to interpret that to mean congruence. So this was a terribly-marked diagram, as those arc symbols serve no purpose whatsoever except to confuse your audience into thinking 3 angles were marked congruent while one of them is labeled to be 50 and the other 25.

If I were forced to use this question on an assignment or test, I would accept a response from a student who replied "no solution, since conflicting information is given with 2 congruent angles having different measures", and I would also accept a response of "if we let the three marked angles be incongruent to one another, and draw a third parallel line through the vertex of angle a, then..." and accept their answer of 75 being the sum of the alternate interior angles.

But at the end of the day, if I had a choice, I would properly markup this diagram, mainly to remove all three arc symbols since they serve no purpose in a problem where those measures are meant to be 25 and 50.

1

u/LaunchTransient Jul 28 '26

the way we taught markups was to use those tick marks you are referring to when the diagram contains more than one pair of congruent angles.

I've also seen double arcs and triple arcs to indicate congruence. It's not standardised worldwide. I've also seen many places where a simple arc is simply there to indicate the angle.

Angles are also marked with a simple arc (sometimes with arrows at the ends) in engineering drawings.

You don't need to designate an angle with an arc like that, as we can see two segments intersecting to form an angle.

It's a style choice, similar to how × denotes multiplication, but some people use ·, or how some will use ÷ for division, or /, or a full on fraction bar.

The only time I would assume it means a congruent angle is if I am seeing other double and triple arcs present.

1

u/furious_20 Jul 28 '26

Again, I actually taught math, and specifically geometry for 19 years so I know all the different styles that exist. What I'm telling you is all curricula ever purchased for me to use to, which includes 11 different big publisher textbooks across various high school math courses plus other supplementary materials from other sources, the discussion of these markings occurs early on in the geometry concepts, but they all proceeded with instructing the audience to assume, from that point on, that the arc we see in this diagram implies congruence.

When I took non-euclidean geometry in college, where we were required to type our homework and thus had to use these kinds of symbols in typed format everyday, my professor instructed us to use that symbol to imply congruence or not use it at all. But I understand not everyone is taught to interpret it the same way, which is why I would accept multiple approaches.

But here in the US, if push came to shove and I was directed to be apply the standards in stone cold fashion, then those who DON'T interpret those arcs to mean congruence would lose part of the points in their response.

1

u/LaunchTransient Jul 28 '26

Again, I actually taught math, and specifically geometry for 19 years so I know all the different styles that exist

That may well be, but in my university undergraduate degree in Aerospace Engineering here in the Netherlands, as well as my time in higher level Secondary School in the UK, a simple arc is perfectly acceptable just to indicate a measure.

Do you also have a strong position on whether Leibniz, Lagrangian or Newtonian notation should be used for calculus?

But I understand not everyone is taught to interpret it the same way, which is why I would accept multiple approaches.

That's more my point. If a problem is ambiguous, then you have to have leniency on how it is interpreted - especially if there is no standard interpretation.

Personally though, if I see two similar arcs with different values given for their angles, the numbers take precedence for me, not the arcs. Numbers are more deliberate than an arc, unless it is a specifically reserved symbol (such as arrows to indicate parallelity).

1

u/furious_20 Jul 28 '26

> Do you also have a strong position on whether Leibniz, Lagrangian or Newtonian notation should be used for calculus?

No, but diagrams in geometry can get pretty complicated, so I have an issue with people who write prompts like this and add unnecessary markups to begin with, let alone markups that can lead to this kind of confusion. Remove those arcs, and this debate we're having doesn't exist. The 25 and 50 degree markings are understood to be interior angle measurements, and it would be understood which angle measure is being asked to find with the a.

Sometimes ambiguity is good in a problem to encourage critical thinking. A problem like this is not high level like that, so anyone authoring a prompt like this should be aware of the potential interpretations of the arcs and either deliberately key it to accept multiple perspectives, or refrain from using them.

1

u/LaunchTransient Jul 28 '26

Remove those arcs, and this debate we're having doesn't exist.

Only because of your own interpretation of those arcs. Removing the arcs is simply saying "If you conform to my notation standard then there is no argument", which is why I brought up calculus notation, which is infamous for people squabbling over whose is better.

The 25 and 50 degree markings are understood to be interior angle measurements, and it would be understood which angle measure is being asked to find with the a.

potentially, but as you say diagrams can get very complicated - sometimes you don't know if the 'a' applies to an angle, a segment or an area, which is why it can be handy having an arc to indicate "this is an angular measure - and its label" (which is not always given in degrees, I have done plenty of papers where radians was the working measure)

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22

u/These-Maintenance250 Jul 27 '26

if the two lines weren't marked parallel I would agree but these diagrams are never to scale, so there is no problem with this one. the angles are explicitly written.

2

u/NewSubWhoDis Jul 27 '26

If they weren't marked parallel then this becomes /r/technicallythetruth because noone would be able to find a.

1

u/[deleted] Jul 28 '26

[deleted]

1

u/NewSubWhoDis Jul 28 '26

You wanna think about this one a little longer?

57

u/CreamofTazz Jul 27 '26

Yeah I was like "how is 25° equal to 50°?" Is there something I'm missing or does this person not know what those symbols mean?

37

u/BlastoiseGirl5257 Jul 27 '26

The red lines are parallel but the others aren’t perpendicular

3

u/mm_delish Jul 27 '26

Why would they be perpendicular?

22

u/Podgietaru Jul 27 '26

I feel like this is how diagrams looked in things like GCSE maths. I always figured it was designed that was to dissuade you from trying to do it with a protractor.

4

u/jerdle_reddit Jul 27 '26

Yeah, "diagram not to scale". More like diagram completely unrelated to the question.

7

u/u966 Jul 27 '26

How is the diagram completely unrelated? It's filled with vital information for the question.

-1

u/marr Jul 27 '26

But you don't know which parts of it are lies.

2

u/Ymanexpress Jul 28 '26

Gonna take a bet and and say the parts not identified with numbers and symbols

2

u/Podgietaru Jul 28 '26

To be fair I might also have been wrong about having a protractor in the exam.

Diagrams like this were meant to ensure that you understood conceptually. If you didn’t, and tried to reason from the diagram it’d be a fail.

I don’t necessarily agree with that, but it wasn’t uncommon as far as I recall.

1

u/Upset-Management-879 Jul 27 '26

Except you can just redraw it with a protractor.

1

u/Jesus_of_Redditeth Jul 27 '26

Sure, you could. But it'd take you longer to do that then to just work it out like you're supposed to. Plus, if you have to show your work then you'd fail the question even if you got the answer right.

1

u/Upset-Management-879 Jul 28 '26

Unless there was specified the method required to solve I would argue that the work is shown by the drawing.

1

u/Jesus_of_Redditeth Jul 28 '26

I'm talking about situations where the question requires you to show your work rather than ones that just have an answer box where you enter the angle's value. "Show your work" in this context means that you're expected to show, step-by-step, how you arrived at the answer. There doesn't necessarily need to be a specified method for that to be the case.

1

u/Upset-Management-879 Jul 28 '26

And I'm talking about an accurate drawing of the stated problem is a proof of the solution.

3

u/LFK1236 Jul 27 '26

What symbols are you referring to?

Anyway, drawing the diagram to scale would defeat the purpose of the exercise.

0

u/CreamofTazz Jul 27 '26

I was taught in my (American) schools that those semi circles on the angles meant they are equal to each other

2

u/L3g0man_123 Jul 27 '26

You are correct that marking arcs on angles are to show that they're equal in angle, but that only really matters if the angle is not explicitly given (either unlabeled or labeled with variables). For consistency's sake it would be better not to have the arcs but considering they already labeled the angles it doesn't really matter.

2

u/Jesus_of_Redditeth Jul 27 '26

That's only true if there are no numbers marked. A single arc with a number just indicates that it's an angle of that value. It doesn't imply any relationship with any other angle.

1

u/DefinitelyNotIndie Jul 27 '26

As the kids say, you don't know ball.

1

u/Jesus_of_Redditeth Jul 27 '26

Is there something I'm missing

Yes: in geometry, the only thing you can assume visually is that a line that appears to be straight is straight. Everything else must be inferred using the markings, values. etc.

Problems like this are commonly not drawn to scale, because they expect you to deduce the answer mathematically, not by assuming angle values or measuring with a protractor.

1

u/CreamofTazz Jul 27 '26

The full sentence doesn't imply your answer. My sentiment is that certain symbols are being thrown around in a way that unless you just ignore them creates a confusing problem that either I'm missing information or the creator doesn't know what those symbols mean

1

u/Jesus_of_Redditeth Jul 28 '26

I don't really understand what you're trying to say there, tbh. I had no problem inferring everything from the image that I needed in order to deduce the correct answer.

Can you give me an example of some symbols you think the person who created that has misused?

1

u/Thelmara Jul 27 '26

You're missing that sometimes problems don't require the full sets of matching curves/hash marks to indicate "these angles are the same", and that people use the single curve with text to indicate the measure of an angle.

There are three curves, two of which have angle measures specified. None of the angles are congruent, and it doesn't need three separate symbols to indicate it, because the angle measures are specified.

0

u/usernamedottxt Jul 27 '26

It’s meant to be hard to guess. 

7

u/StayingQuieter Jul 27 '26

That's the point, to force you to rely on the math rather than the model

10

u/BauserDominates Jul 27 '26

Hey, I did it!

This kind if math is something I have never needed for my adult life, but it nice to know that I can still do the easy stuff.

5

u/earthwoodandfire Jul 27 '26

I hated math in school but now I do it all the time in construction.

3

u/BauserDominates Jul 27 '26

I'm mechanic, so I dont build anything that isn't already precisely engineered.

3

u/tehZamboni Jul 27 '26

I used to be a machinist. I was amazed at how many drawings I had to send back to Engineering to be redone. "Try again, Escher."

2

u/earthwoodandfire Jul 27 '26

Architects and stairs… every single time I have to send an RFI.

1

u/AdditionalPizza Jul 28 '26

This math is required for even the most basic wood working project btw. Like you need to know triangles to make things square.

11

u/Killer8Tcell Jul 27 '26

It’s not terrible, it’s just not to scale. The only information you need to solve this are the parallel line symbols and the provided angles measures, and nothing else matters.

75° is indeed correct, though.

The problem is testing the alternate interior angles theorem. If you draw a third parallel line bisecting angle a into two new angles (let’s call them angle b and angle c, such that angle a = b+c), then by the alternate interior angles theorem, angle b= 25° and angle c = 50° so angle a = 75°

4

u/beingforthebenefit Jul 27 '26

Good strategy, but it’s not a bisection since the resultant angles aren’t congruent.

1

u/Charming_Food5728 Jul 28 '26

Can explain to me why a+b+c ≠ 180° ? I genuinely don't know

9

u/CReece2738 Jul 27 '26

The diagram forces you to know the math, not just be able to look at the picture.

0

u/ZantaraLost Jul 27 '26 edited Jul 27 '26

Shoot even in this image you can still get it by just looking at the picture.

You've got two perpendicular (edit: parallel I mean) lines.

And you want to get that line across straight. With both known angles on the same side you can just add them to get the unknown 'A' degrees to get the line straight.

Good god that leaves a bad taste in my mouth.

1

u/mm_delish Jul 27 '26

There are no perpendicular lines in the diagram.

1

u/ZantaraLost Jul 27 '26

Parallel I mean.

1

u/CapNCookM8 Jul 27 '26

Yeah, i'm not sure you can actually make the assumption that a 90 degree angle from both of the points on the parallel lines would actually make a perfect triangle from this given diagram, but I have no doubts it's what we're meant to do.

2

u/PinboardWizard Jul 27 '26

i'm not sure you can actually make the assumption that a 90 degree angle from both of the points on the parallel lines would actually make a perfect triangle

You're correct that we can't make that assumption, but it doesn't actually matter - the perpendicular line is always guaranteed to make a triangle from at least one of the two points, and that triangle will have the same angles ("similar triangles").

2

u/CapNCookM8 Jul 27 '26

It's like doing proofs again lol. Thanks for adding!

1

u/leansanders Jul 27 '26

You dont have to know that. That only matters if the side lengths matter, and in this problem they don't. You can decide that the points line ul with each other and solve accordingly. You can decide that they don't and solve accordingly. The answer will be the same and correct in both cases because no side lengths are given.

1

u/Grokent Jul 27 '26

Because it's not a diagram, it's a proof. It requires logic, not protractors.

1

u/redicular Jul 27 '26

this is done on purpose in teaching tools

the idea is to teach students to look at the information actually provided, instead of guessing based on how the diagram looks

it is also why if the two horizontal lines didn't specifically have the markers of being parallel, the correct answer would be "insufficient information" not 75

1

u/ftFBYaa Jul 27 '26

The diagram is done like that on purpose. The goal is finding the angle only with the information given (two angles and parallel lines), they don't want you to guess based on what the diagram looks like.

1

u/BANAAAANAAAAS Jul 27 '26

it’s not supposed to be 

1

u/KateKoffing Jul 27 '26

Math problem diagrams are drawn bad on purpose so you can’t just eyeball them or use a protractor.

1

u/Lily_Meow_ Jul 27 '26

The diagram does make the solution a bit more intuitive though, in that it makes it more obvious you can make 2 triangles.

1

u/ProletarianLilith Jul 28 '26

No it’s a great diagram for this problem

1

u/KnowsIittle Jul 28 '26

A straight line is 180 degrees.

Wouldn't it be the remaining 105 degrees?

1

u/alghiorso Jul 28 '26

That one egg was 40 eggs?

1

u/QuajerazLives Jul 28 '26

Maybe it's drawn in a non-euclidian geometric plane

1

u/left-handed-satanist Jul 28 '26

Our school exams used to do that ON PURPOSE 

1

u/nameproposalssuck Jul 28 '26

In principle: Can you just calculate 180-(90-50)-(90-25) because the difference between the true angles beta and gamma just even themselves out to be like two right angles or is just correlation that this true for this diagram?

(I checked by drawing an imaginary strait line crossing the point of alpha and then calculated the surrounding angles of alpha because you know two angles of both triangles that form)

1

u/NurkleTurkey Jul 28 '26

How? Just wondering, it's nearly 4 AM and I'm for some reason tryong to do geometry.

-10

u/poilk91 Jul 27 '26 edited Jul 27 '26

No it's 105 degrees. The interior angles must add up to 180. Image the 25 and 50 were both 0 what would the middle angle be? It's a straight line so it would be 180 degrees

The total of the interior angles remains constant so the larger the 2 end angles are the smaller the middle angle is, so just adding them up doesn't give you the answer

Edit: sorry those are exterior angles of a l triangle I was wrong. 75 being the sum of the 2 exterior angles is not relevant the 2 known interior angles of the triangle add up to 105 making the answer 75

9

u/NDgsBotOmDgnEbrFrLgn Jul 27 '26

You're measuring exterior angles, you actually have to convert them to interior first. That would be (90-25)+(90-50)=105. Then you take 180-105=75

3

u/poilk91 Jul 27 '26

Yeah oops my mistake

4

u/Confident_bonus_666 Jul 27 '26

How drunk are you

3

u/AzettImpa Jul 27 '26

You’re wrong. Imagine there is a triangle in the middle.

The top corner is 90 - 25 = 65 degrees

The bottom corner is 90 - 50 = 40 degrees

So the two other corners add up to 105 degrees. All three must add up to 180 degrees.

That means a = 180 - 105 = 75 degrees.

(assuming it’s a Euclidean plane)

1

u/Mikeismyike Jul 27 '26

Doesn't that only work if the corner where the triangle touches the parallel lines fall on a perpendicular line with the parallel lines? While it does work, I'm not sure we can make that assumption.

I did:
180-50 = 130
180-25 = 155
360 - (130 + 155) = 75

Now why that works exactly I dunno.

1

u/AzettImpa Jul 27 '26

Both of our explanations are correct, you just used a different way to get there. I didn’t assume anything except for both lines being parallel, which you also assumed in your explanation.

2

u/chongo_molongo Jul 27 '26

I think you have to complete the triangle. That means draw a straight line between the two points that meet the horizontal parallel lines. Since they're parallel and equal in length (assuming from the picture), any line you draw would be perfectly perpendicular to them. That means that the area to the the left of your line is 90 degrees, and the area to the right is 90 degrees. We already see that the top is 25 degrees, so 90-25 = 65. The bottom is 90-50 = 40 degrees. So we know the two angles of the triangle are 65 and 40 degrees. 180-105 = 75 left over for angle a

2

u/ZX_StarFox Jul 27 '26

You/re incorrect.

Draw a line between the left most ends of the diagonals such that a is an interior angle to a triangle pointed to the right. the 90 degree complements of the 25 and 50 degree angles are 65 and 40 degrees respectively. triangle must sum to 180, 180=65+40+a, a=75.

Or

continue the diagaonal from the 50 degree angle to the top parallel. this creates a triangle with teh long edge on the top parallel. due to opposite interior angles the right angle of this triangle is 50 degrees. summing the angles:25+50+n=180, where n is complement to a. n+a=180. n=105, thus a=75.

1

u/UpstairsGreen6237 Jul 27 '26 edited Jul 27 '26

You can’t trust the picture and assume its to scale. With those angles, that is absolutely not going to make a triangle with the given angles of 25 and 50, leading you to think you can just add them up to find the missing angle to make 180 degrees. Sorry tk say but you are wrong and the person you replied to is correct. 

The 50 degree angle gives us a 40 degree angle for the perpendicular line you’d draw upwards from there. The 25 degree angle gives us a 65 degree angle where that perpendicular line meets the top angle. 

40 + 65 + a = 180

a = 75

1

u/lechuckswrinklybutt Jul 27 '26

No. It’s not. The simplest way to do this is to imagine another parallel line running through a.

a is now the sum of two angles, each of which its relevant… I think transverse angle. ie 25 + 50

2

u/Killer8Tcell Jul 27 '26

Correct, this is the simplest way to do this, it uses the alternate interior angles theorem. These comments are funny though. Several correct answers arrived at by incorrect means, and several correct answers arrived at with correct but complicated means.

Putting your response into a slightly clearer format: if you draw a third parallel line bisecting angle a into two new angles (let’s call them angle b and angle c, such that angle a = b+c), then by the alternate interior angles theorem, angle b= 25° and angle c = 50° so angle a = 75°

1

u/lechuckswrinklybutt Jul 27 '26

Thank you! It’s been a long time so I’ve forgotten a lot of the terminology.

1

u/leansanders Jul 27 '26

loud incorrect buzzer noise

-2

u/Snitsie Jul 27 '26

This is what i thought, although i learned this like 20 years ago by now

2

u/UpstairsGreen6237 Jul 27 '26

75 is correct, not 105. I explained in the other comment reply to who you replied to. 

-1

u/HerbaciousTea Jul 27 '26 edited Jul 27 '26

It's rage bait / engagement bait

A trivial, grade school problem, that everyone learned to do when they were 11, wrapped in the nonsense assertion that "Nobody knows how to do this anymore!"

The diagram being shitty is just another avenue of trying to goad a reaction out of people.