Random math thing

Let's say that
A = B

ok and now we multiply it by A

A^2 = AB

then we subtract B^2 from both sides

A^2 - B^2 = AB - B^2

And now we edit it a bit

(A-B)(A+B) = B*(A-B)

We divide both sides with A-B and we get

A+B = B

Let's say that A=1=B and we get

1+1 = 1
2 = 1

What's wrong, help !?


(and yes I know what's wrong but let's see if you find it too)

image: dividebyzero
Comments
63
Let's say that
A = B

(A-B)(A+B) = B*(A-B)
a-b = 0

0 x (A+B) = B x 0
0 = 0
you can only divide by A-B if it's different from 0 so A should be different from B
you found it pretty fast congratz :)

although I think raichu means the same, he just didn't put it so clearly :D
Parent
Quote1+1 = 1
2 = 1


i found it
i skimed over your text but i think this line is wrong (A-B)(A+B) = B*(A-B)
read my edit: am I doing it right?
Parent
that line is correct but you were right that dividing with a-b isn't allowed, because you can't divide by zero
Parent
u divided by 0.
A-B=0
so I was right?
Parent
yes but it is not just that.. A^2-B^2 = 0 too therefore he proved 0=0
every line which involves A-B equals 0 and also A^2-B^2=0 and AB-B^2=0 so everything after the second step is the same as 0=0
Parent
surely you can operate with zeros, but you can't just divide with them :)
Parent
ye well I remember this math question but there was more wrong with it then just dividing by 0.. give it anything you do after dividing by (A-B) is automatically wrong.
Parent
ofc but that all follows because of the dividing
Parent
afaik there were some more errors in the reasoning of that question even before the dividing but I dunno anymore and I can't be bothered right now anyway xD
Parent
nee, otherwise it should be correct, only the dividing by zero isn't allowed
Parent
okee, I believe you :D
but too be true it is all bullshit, maths are based on 5 presumptions(axioms) which can't be proven.
Parent
in uni we tried to make own number systems based on those axioms, but they didn't really work, one or more of those never applied, and only in our current system all of them work.

I found it kinda boring stuff, so don't ask me more, I don't even remember much of it anymore :/
Parent
QuoteWhat's wrong, help !?

the answer of course
oh, I always thought that 2=1 explains why I alwas sucked in school :(
Parent
no sorry it doesn't ;p
Parent
then why did I suck :( ?
Parent
if only I knew ;p if I knew it, it could be the same cause as my maths suckage, and I could fix it
Parent
well I was fooling you, I didn't really suck at school :)

so maybe you don't suck there either ;)
Parent
If my teacher wouldn't be so boring I could try to pay attention ;p
Parent
Let's say your a dick, what's wrong?

answer: nothing
the definition u set in the first step kills all the steps u take after that.
Most of them are actually correct :)
Parent
1+1 = 2
thats wrong
everybody knows 1+1=11
devide by zero and the problem will be gone.
you can never devide by (a-b) if a=b
uber question .
ask perfo
aslong as A=B its wrong (dividing with zero)

but tricky !! :P
yup

took me some time to realize it also, so wanted to see how ppl in here manage in it :)
Parent
tbh i´m not sure if i would have realized it without your random pic ;D
Parent
haha :D

I added it later, saw plekter use it in some other journal so I thought it suits well in here :D
Parent
Math boi yo
gimme the turning point from this function:
1/k * e^-1/2x²+kx

thats what i mean http://www.rither.de/images/mathematik/analysis/differentialrechnung/wendepunkte/wendepunkt.gif
Find dy2/d2x = 0?
Parent
x = 0
k =/= 0
Parent
for 2nd derived is = 0
or 2nd differential = 0
dunno the english terms rly.
ur function is f(x)
so f''(x)=0 gives the x-coordinate of the turning point
Parent
i know but try to calculate this ^^
Parent
x is approximately .838729? Derived this from -4 ln(x) = x^2. Does that number have any special meaning/can it be expressed in a more "natural" form like e^n? I'm not certain what it represents, but it is clearly independent of k (though the y value obviously will be a function of k).
Parent
2! = 2
3! = 6
4! = 24
Parent
fakultäten oder wie die teile heissen sind easy ^^
5! = 120 ?
Parent
jop :P

5! = 1*2*3*4*5

npnp
Parent
I stand corrected!
Parent
we learned that j^2 = -1 :ooooo
Parent
so did I (since I'm in electrical engineering), since electrical current is represented by the symbol i, so to avoid confusion in AC circuits involving the use of complex phasors it was decided that "j" would signify the imaginary unit. However, to satisfy these math nerds, I use "i" on occasion :P
Parent
touché, I've studied advanced engineering in electronics as well, but I got a bit bored with that and atm I'm doing something else :)

we used "j" as well ofc
Parent
not so random pic :/
sry ^^

I added it just later :)
Parent
actually its e=mc²
Parent
Quote
1+1 = 1
2 = 1


YOU IZ NOT GOOD IN MATHS :DD my math teacher would give you 0 points and write a nice comment that you have to go back to 1st class ;)) like he did it to my friends
Back to top