What is wrong with the following proof Let xy Then x2xy x2y2

What is wrong with the following \"proof\"? Let x=y. Then,

x^2=xy,

x^2-y^2=xy-y^2,

(x+y)(x-y)=y(x-y),

x+y=y,

2y=y,

2=1.

Solution

IN going from third step to fourth step we dividied both sides by x-y but x-y=0 since x=y

But we cannot divide by 0. So going from third to fourth step is wrong.