# What's the mistake here?

1. Apr 29, 2012

### Hernaner28

What's the mistake here? hehe

http://a7.sphotos.ak.fbcdn.net/hphotos-ak-snc6/64102_341098562596296_100000884664248_973353_615500462_n.jpg [Broken]

Last edited by a moderator: May 5, 2017
2. Apr 29, 2012

### AlephZero

$2(a^2-ab) = 1(a^2 - ab)$
Therefore either $2 = 1$ or $a^2 - ab = 0$
And $a^2 -ab$ is equal to 0, of course.

3. Apr 29, 2012

### Mentallic

Say you wanted to solve the quadratic $x^2=x$. You wouldn't begin by dividing through by x because that assumes $x\neq 0$. If x=0 then you've just lost that solution.

In short, dividing by zero is bad.

4. Apr 29, 2012

### Hernaner28

Hmm I see... it was stupid from me not realising that.. lol :D

Thanks!

5. Apr 29, 2012

### I like Serena

Don't try this at home...

6. May 2, 2012

### Akshay_Anti

In the first line, you say a=b
and therefore a^2=ab. a^2-ab=0.
You are dividing by zero even though it's not defined in mathematics. That's the mistake... :D