How about this one ?

x = y

x² = xy

x² - y² = xy - y²

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

x + y = y

2y = y

2 = 1

WAIT !

Don't

look

yet !

It's

really

quite

easy !

Go

back

and

try

it

again !

Beware

of

x - y !