2=1?

Let a = b

a*a = a*b
a*a - b*b = a*b - b*b
(a-b)*(a+b) = b*(a-b)
a+b = b
b+b = b (Since a = b)
2b = b
2 = 1

:) nice result to confuse people... the error is in going from line 3 to line 4 where we cancel out (a-b). Since a-b is zero therefore division by a-b is not defined.