What's wrong with these equations?

[kacete]

1=2? -1=1?

First:
1-1=0
2-2=0

1-1=2-2

1*(1-1)=2*(1-1)

[1*(1-1)]/(1-1)=[2*(1-1)]/(1-1)

1=2

Second:
-1=-1

1/-1=-1/1

sqrt(1/-1)=sqrt(-1/1)

sqrt(1)/sqrt(-1)=sqrt(-1)/sqrt(1)

1/i=i/1 note: i=sqrt(-1) complex number

i/(i^2)=i note: i/(i^2) equals 1/i as in 3/9 equals 1/3

i/-1=i note: i^2=-1 complex number

-i=i

i*(-i)=i*(i) note: preserved equality of equation

-1=1

[element4]

The error of your first example is that devision by zero is undefined, 1-1=0.

The second example fails duo to use of the identity \sqrt{\frac ab}=\frac{\sqrt a}{\sqrt b}, since this is only valid for a,b>0. See wikipedia (http://en.wikipedia.org/wiki/Exponentiation#Failure_of_power_and_logarithm_iden tities), for more info.

See more similar "proofs" here (http://en.wikipedia.org/wiki/Invalid_proof).

[kacete]

Now that was simple, thank you. I saw this around and it was messing with me. Guess math can't be tricked. Never would have guessed something similar was already on wikipedia. Thank you!