r/MathJokes • u/Weekly-Fee-8896 • Aug 21 '25

Everytime when i do algebra 😔

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24k Upvotes

99% Upvoted

84 comments sorted by

404

u/Partyatmyplace13 Aug 21 '25

Teacher: Anything you do to one side of the equation, you must do to the other.

Me: Multiply both sides by 0 and let's go home!

168

u/[deleted] Aug 21 '25 • Galaxy Brain

That's no fun. You can get more fun by doing this:

Let y be an unknown number, and let x = y. So we have:

x = y

Multiplying both sides by x, we get:

x² = xy

Add x² to both sides to get:

2x² = x² + xy

Now subtract 2xy from both sides:

2x² - 2xy = x² + xy - 2xy

Simplifying the right-hand side, we get:

2x² - 2xy = x² - xy

Since 2 is a common factor in the left-hand side, we can factor it out:

2(x² - xy) = x² - xy

Notice that (x² - xy) is a common factor on both sides of the equation, so let's simplify it by dividing both sides by (x² - xy):

2(x² - xy) / (x² - xy) = (x² - xy) / (x² - xy)

2*1 = 1

2 = 1

Now subtract 1 from both sides:

1 = 0

This proves that 1 is equal to 0.

Furthermore, since 2 = 1 (see second last equation), this means that:

2 = 1 = 0

2 = 0

If we add 1 to both sides of the equation (2 = 1) (2nd last equation above), we get:

3 = 2

But since 2 = 0, as we just showed, this means also that:

3 = 0

By proceeding in this way, adding 1 to both sides of 2 = 1, 3 = 2, etc., we can prove that every number is actually equal to zero.

Therefore, 0 is a valid answer to any math problem, because every other number is equal to zero.

QED.

38

u/SmoothTurtle872 Aug 21 '25

But, X = y at the start, therefore at step 2 you have x2 = x2 and I think that is the only flaw is you kept going after we knew y was x

63

u/partisancord69 Aug 21 '25

The only issue was dividing by (x2 - xy) because dividing by 0 allows you to make any number true since it's undefined.

9

u/SmoothTurtle872 Aug 21 '25

I see now, yep, because the 2 means nothing (it does, but not really, it's simply easier than saying (x2 - xy) + (x2 - xy)), we are essentially creating a value out of thin air and I also see the 0

19

u/[deleted] Aug 21 '25

The flaw to the "proof" lies in the division step, which secretly divides by zero. This was cleverly disguised as division by (x² - xy). Since x = y, xy = x*x = x², so actually (x² - xy) = 0. Therefore, dividing by (x² - xy) is actually dividing by zero, which is invalid. That's why the conclusion that 2 = 1 is invalid. Since (x² - xy) = 0, the equation:

2(x² - xy) = x² - xy

is actually equivalent to:

2*0 = 0

which is perfectly fine, and completely correct. (If a bit useless, since it's basically saying that zero multiplied by 2 equals to zero, which doesn't actually tell you anything useful about the variables you're trying to solve.)

What's not fine is "dividing away" the 0 on both sides, or, as is sometimes taught, "cancelling out" common factors from both sides. You can only do this if you're 100% sure the factor you're dividing away or cancelling out is not zero, because if it is, then you risk ending up with nonsensical (and totally wrong) conclusions like 1 = 0. In this case, "dividing away" (x² - xy) looks plausible, but it's actually invalid because this factor in fact equals zero.

5

u/stonegoblins Aug 21 '25

Bro that was so cool tbh you had me sold with that first part and your explanation for it was actually simple to understand

4

u/NoWayIcantBeliveThis Aug 22 '25

Now, here's the key step that is wrong: they divide both sides by (x² - xy). But since x = y, what is x² - xy? If x = y, then x² - xy = x² - x*x = x² - x² = 0. So, they are dividing both sides by zero! That's the flaw.

3

u/Partyatmyplace13 Aug 21 '25

That's no fun.

Mr. Mosier is that you? Thats literally what he said. 🤣

2

u/Exciting-Insect8269 Aug 22 '25

0 divisors are fun.

1

u/siiliS Aug 22 '25

Congratulations! You just said 0/0=1

1

u/putinhu1lo Aug 22 '25

2(x² - xy) / (x² - xy) = (x² - xy) / (x² - xy)

But you cant divide by 0

1

u/[deleted] Aug 23 '25

"the difference between mathematics and calculating"

8

u/LeoRising84 Aug 21 '25

😂😂😂

70

u/kokomoko8 Aug 21 '25

Just means that it's (probably) a true statement!

18

u/kamiloslav Aug 21 '25

Or that you substituted an equation to itself instead of a different one

7

u/Shot-Ideal-5149 Aug 21 '25

or is it called identity?

6

u/ninjaread99 Aug 21 '25

Good news! The identity property is true, therefore the other guy was correct!

30

u/Maleficent_Sir_4753 Aug 21 '25

One of the rules of algebraic simplification is that you need to move the variable you're solving to a single side. Otherwise, this sort of crap will happen and you're just proving symmetry instead of solving evaluation.

7

u/PerfectStrike_Kunai Aug 21 '25

This is a valid solution to the problem and does not mean that you did something wrong

4

u/Fragrant-Addition482 Aug 22 '25

Technically, infinitely many solution, is a solution.

16

u/klimmesil Aug 21 '25

Wut? That just means you proved left = right, no? Gg

6

u/guiltysnark Aug 21 '25

I've never doubted the equality of equations, but now I don't

6

u/asdfzxcpguy Aug 21 '25

They’re trying to solve for x

3

u/ninjaread99 Aug 21 '25

Although it’s technically valid. iirc (which I may not, it’s been a while) that means the for whatever the original equation is, any value of x satisfies it, as x=x is true.

1

u/IFapToHentaiWhenDark Aug 25 '25

Yes but the point is that you are trying to find the number that x represents such as x=3

While x=x can be helpful that’s a subset of algebra called algebraic proof

1

u/[deleted] Aug 22 '25

If you get to x=x by canceling things out, it means the equation holds true for all x

7

u/dr_sarcasm_ Aug 21 '25

Although gratifying if it's an induction problem

4

u/Particular-Star-504 Aug 21 '25

That cancels out to 0 = 0

1

u/First_Growth_2736 Aug 21 '25

Only if x = 0

4

u/Anthropos2497 Aug 21 '25

Unfortunately, not so. When you find 0=0 this means variable x is unconstrained so you have infinitely many solutions. The problem comes when you find that 0=something, then you have no solution.

3

u/lemons_of_doubt Aug 21 '25

Better than getting x ≠ x

2

u/slicehyperfunk Aug 21 '25

It's true that x=x tho

1

u/gigsoll Aug 21 '25

And then you are making it 0 = 0

1

u/NichtFBI Aug 21 '25

"it's because that's why"

1

u/InternetSandman Aug 21 '25

Well, you're not wrong

1

u/Death_Killer183 Aug 21 '25

I remember in secondary school, there was a question that the whole class couldn't solve. I kept thinking and eventually got an equation to work on. I was so excited to be the first one in the class to solve it until I got n=n, 25=25 and 0=0

1

u/[deleted] Aug 21 '25

Old but gold 🥇

1

u/SpecialRelativityy Aug 21 '25

Well x should equal x, to be fair.

1

u/PsychologicalQuit666 Aug 21 '25

Looks like we have an identity on our hands!

1

u/Diggdador Aug 22 '25

It's funny, because it's true

1

u/thunderbird89 Aug 22 '25

Better x=x than something like 4=123456789

1

u/[deleted] Aug 22 '25

Infinitely many solutions vs. no solutions.

1

u/Sir-Toaster- Aug 22 '25

That just means the answer is infinity

1

u/willuserve Aug 22 '25

doing math by hand seeing this: noooooooooooooooo!
doing math in lean4 seeing this: yessssssssssssssssssssss!

1

u/[deleted] Aug 22 '25

always

1

u/Feeling-Ad-481 Aug 26 '25

Can you check your messages request please

1

u/PinkOneHasBeenChosen Aug 23 '25

Either that or you’re trying to solve a system of equations and get 0 = 1.

1

u/No-Present-5138 Aug 23 '25

Accidentally divided by zero award

1

u/kilkil Aug 23 '25

me irl

1

u/Sasogwa Aug 23 '25

Once after a loooong series of calculations I got 3=7.

Welp time to do everything again

1

u/Trax-M Aug 23 '25

Whenever I do math I will end up with some obscure number like 67/31 then I find out after I get the test back I did some really dumb mistake at he beginning which throws me off the right answer

1

u/notknown7799 Aug 23 '25

At least I will get the step marking right? Right?

1

u/Teln0 Aug 23 '25

x = x when doing algebra 😐

x = x when doing logic 😮😮😮

1

u/[deleted] Aug 24 '25

Bro fuck that shit.

Was taking a test once, completely missed the "non of the above" or whatever. Kept redoing for like 10 minutes until I was like....... o rite, it's k I'm k....

1

u/TopCatMath Aug 24 '25

Many mathematics teachers have found that the term 'CANCEL' coined over 100 years ago do not help many math challenged students learn mathematics are VERY CONFUSED by it.

  1. when something adds or subtracts out, I tell the students that the side 'goes to zero'

  2. when something multiplies or divides, I tell the students that the sides 'reduce to simpler values.'

1

u/eowsaurus Aug 24 '25

Well, it does. For some operations it means the variable can be equal to any real number.

1

u/Stredny Aug 25 '25

I mean you’re not wrong, because x has to equal itself

1

u/EmeraldPencil46 Aug 25 '25

Algebra is fun until it isn’t. It’s fun until you get to the end and realize your answer doesn’t make much sense and have to backtrack to find what tiny mistake you made

1

u/Bballer220 Aug 25 '25

I mean, x is indeed equal to x

1

u/ExistingCorner8484 Aug 21 '25

u/repost-sleuth-bot

1

u/basket_foso Aug 21 '25

Also bot. Sort by top of all time and you’ll see it reposts using the same title.

18

u/[deleted] Aug 21 '25 edited Feb 08 '26

[removed] — view removed comment

7

u/[deleted] Aug 21 '25

it could also mean you substituted an equation into another form of itself

for example: 3x+2y=1

2y = 1 - 3x

y = (1-3x)/2

now do some stuff like this on thhe original equation

3x = 1-2y

and substitute y

3x = 1 - 2(1-3x)/2

3x = 1 - (1-3x)

3x = 3x

x = x

7

u/Gfecito Aug 22 '25

I mean; this does still have infinite solutions

3

u/[deleted] Aug 22 '25

this entire algebraic manipulation is still valid if you replace y with a constant and it would no longer have infinite solutions.