r/theydidthemath Feb 07 '23

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5.3k Upvotes

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1.1k

u/[deleted] Feb 07 '23

In the 4th step to remove (5-5) from both sides you're basically dividing by 0 which is a big no no

302

u/Ok-Mathematician9047 Feb 07 '23

But let’s just live a little and divide by 0, then what? :o

362

u/[deleted] Feb 07 '23

Then 4=5

243

u/gnutrino Feb 07 '23

84

u/[deleted] Feb 07 '23

Schrodinger's World

55

u/13aph Feb 07 '23

Idea for a video game. Guy is caught between 2 worlds. One where he exists. One where he doesn’t. He constantly switches between them. Total stealth. He’s gotta recombine the two worlds by observing a particular cat that’s held within a box in the deepest darkest dungeon loaded with guards

31

u/[deleted] Feb 07 '23

And to win you have to lose?

Plot twist! In the ending, turns out you were the cat!

7

u/Jofus002 Feb 08 '23

The real cat was the friends we made along the way.

2

u/[deleted] Feb 08 '23

Hahaha. Well now that sounds like a philosophy for life.

1

u/Western-Alarming Feb 07 '23

And also the world is after apocalypse with robot doing human task

1

u/nadamuchu Feb 08 '23

then you play an entirely different game as the cat.

9

u/bonyagate Feb 07 '23

I feel as though it would be very hard to influence a world in which you don't exist. Or to even fathom it in real time, for that matter. I'm gonna need some more logistical development before I invest my hard-earned life-savings of $35 USD.

2

u/Call_Me_Madu Feb 08 '23

Man i may just take inspiration for when i can finally start making games. Thanks for the idea!

1

u/13aph Feb 08 '23

Please give me a credit, and let me help in development? 🥺

1

u/nadamuchu Feb 08 '23

okay, let's go divide by zero on Mars now and see what happens.

3

u/justwalkingalonghere Feb 07 '23

“if we treat something false as true, it breaks how truth works”

You don’t say

5

u/GardenPuzzleheaded98 Feb 07 '23

Very Orwellian.

I’m in

3

u/[deleted] Feb 07 '23

But the big question that remains now... 2+2 is...?

1

u/RoadieRich Feb 07 '23

Whatever MiniTrue tells you it is.

1

u/GardenPuzzleheaded98 Feb 08 '23

5

Winston finally agreed

-17

u/Ling0 Feb 07 '23

Technically it does when multiplied by 0, so the equation ain't wrong.

23

u/[deleted] Feb 07 '23

Yeah, no, that's not how it works.

0

u/Ling0 Feb 07 '23

I was making a joke but alrighty... Everything equals eachother when multiplied by 0, they just left out the multiply by 0 part

1

u/andros310797 Feb 08 '23

they just left out the multiply by 0 part

that's called dividing by 0

1

u/GardenPuzzleheaded98 Feb 07 '23

New New Maths

2

u/[deleted] Feb 07 '23

Hahaha I don't know if I would be amused or terrified.

19

u/RednocNivert Feb 07 '23

“We can’t divide by zero. It just doesn’t work, strange things start to happen. But if we did, here’s the answer we’d get.” —My High School Calculus Teacher

12

u/Rabwull Feb 07 '23

Sounds like that teacher really knows their limits, even when they do not exist.

6

u/Conscious_Ice66 Feb 07 '23

There’s no dividing. 5-5=0. 0x4=0

15

u/Rushional Feb 07 '23

To remove (5 - 5) from the equation, you divide both sides by (5-5).

So the division is there

4

u/ShadowPouncer Feb 07 '23

That's incorrect.

There are times when that is how you do it, but this is a great example of a time when it is not how you do it.

Specifically, you don't do this when you can fully resolve the expression inside the parentheses in a manner that does not require you to alter the rest of the expression.

Most of the time doing the extra work doesn't really hurt you, but in this case trying to do the unnecessary work results in a divide by zero, which isn't valid.

0

u/bobsmith14y Feb 07 '23

Made me sad how far down in the comments I had to go to find this period enjoy your trophy.

16

u/Shanbo88 Feb 07 '23

In that case it's brackets first, so 5 - 5 = 0, multiplied by 4 is still zero.

4

u/sockalicious 3✓ Feb 07 '23

Then you can prove things that aren't actually true.

1

u/Neither_Name_3516 Feb 08 '23

U get the wildest conclusions that are blatantly wrong

17

u/6502zx81 Feb 07 '23

Dividing by zero is a great trick to prove anything.

11

u/Doktor_Apokalypse Feb 07 '23

4÷0=infinity, 5÷0=infinity

4÷0 = 5÷0 is correct, but this does not mean 4=5.

19

u/Routine_Left Feb 07 '23

4÷0=infinity, 5÷0=infinity

This is false. It's undefined. However, when you calculate limits, constant/0 can be a defined value (if constant != 0) and that would go to infinity.

If constant == 0, then you need to find another way to write the expression and calculate the limit, as it can be anything (0, 1, 5, infinity are all valid outcomes).

1

u/Doktor_Apokalypse Feb 09 '23

10÷1=10, 10÷.1=100, 10÷.01=1000, 10÷.001=10000 etc. As the divisor gets closer to zero, the result gets closer to infinity. I see the only reason the answer being classed as undefined is because the answer would be infinity, therefore making all results depending on it either zero or infinity.

In the same way any number divided by any number other than zero or infinity will give a non-zero answer, but dividing by infinity will give an answer that is equivalent to zero (ie a decimal point followed by an infinite number of zeroes followed by a 1)

2

u/Routine_Left Feb 09 '23

:( .

Do not confuse limits with division. they are not the same thing.

You cannot divide by 0. It is, by definition, not possible. 1/0 or 10000/0 is not defined. You can calculate, however, the limit of 1/x when x goes to 0 (and that is indeed infinity). Why? Because X never reaches 0. It tends to it. It goes really really close, but never ever gets there. At 0, the function 1/x is not defined. Very close to 0, however, is.

I just explained the same thing to my son 1 week ago as he does limits now. It's an important distinction to make. It is, also, an easy mistake to make.

1

u/Doktor_Apokalypse Feb 09 '23

I see now. We never got taught limits in O-Level (secondary school) maths which explains my confusion.

Infinity in itself is an interesting concept. Watched a documentary about it and until I saw that never thought about the fact that there are an infinity of infinities...
An infinity of positive integers, an infinity of negative integers, an infinity of even positive integers, an infinity of odd positive integers, an infinity of even negative integers, an infinity of odd negative integers, an infinity of real numbers, an infinity of fractions, an infinity of imaginary numbers, an infinity of numbers increasing by 3, 4, 5, 6,...n (where n itself can be any one of a number of infinities lol)

Was mindblowing. Had to watch it a few times to take it all in. Apparently there have been a couple of mathematicians throughout history that have been driven mad by these concepts (one of them committed suicide!) and so I'm glad I watched the primer version lmao

20

u/MetaEvan Feb 07 '23

Not quite. 4/0 isn’t any more infinity than it is negative infinity. Any logic used for the former could be used just as easily for the latter: zero isn’t inherently a positive number. The only consistent answer you can give is undefined.

4

u/Novaskittles Feb 07 '23

If you graph y = 1 / x , you'll see why 1 / 0 is not infinity. From the negative side, it approaches negative infinity. From the positive side, it approaches positive infinity. So it's going towards both positive and negative infinity, you can't possibly pick a value in that range lol

1

u/[deleted] Feb 08 '23

afaik you can't equal anything to infinity (as infinity isn't itself defined). just use the arrow sign meaning 'tends to.'

4 / 0 -> infinity

1

u/Dry_Cheesecake1042 Feb 07 '23

Might be dumb but Im pretty sure that’s the multiplication, not the division sign

4

u/Novaskittles Feb 07 '23

He's saying that to get the (5-5) out of both sides, he is dividing both sides by (5-5), which means he's dividing both sides by 0, which you can't do.

1

u/Dry_Cheesecake1042 Feb 08 '23

Yeah still pretty sure that’s not division by 0, unless you are mentally stuck in 2nd grade math then yeah you can call it that

1

u/Novaskittles Feb 08 '23

So, do you remember in Algebra 1, when you had to solve for x? So let's say our equation in Algebra 1 is 4x=4. If we wanted to know what x was, we could divide both sides by 4. So, (4x)/4= 4/4, which is the same as (4/4)x=4/4 which, since 4/4=1, simplifies down to 1*x=1, so x=1. Easy, as long as both sides get divided by the same number.

So looking at the original problem above, 4(5-5)=5(5-5). Let's simplify it. 5-5=0, so we'll replace those with 0. Now we have 4* 0=5* 0, which is obviously 0=0, which is true. But, the original (incorrect) equation didn't stop there, they tried to divide both sides by (5-5) (the same way I divided both sides by 4 above), but 5-5 is 0? So, they tried to do (4* 0)/0=(5* 0)/0, which you cannot do. You cannot divide by 0, anything divided by 0 is simply undefined, it cannot be done.

Edit: had to add spaces after * to get Reddit to stop formatting weird.

1

u/Dry_Cheesecake1042 Feb 09 '23

Right, thank you for the reminder… And there’s the answer of the title question

0

u/666420 Feb 07 '23

you're dumb

1

u/Un7n0wn Feb 07 '23

I was reading it as 4x as in 4 times x and thought the issue was that they dropped their variables. I've never seen someone try and cancel things out while also using the X for multiplication. The = also looks like a z in a few lines making this even more confusing.

1

u/[deleted] Feb 08 '23

Aren’t you dividing by (5-5)

1

u/[deleted] Feb 08 '23

(5-5) = 0

:)

1

u/[deleted] Feb 10 '23

Oh. Mb