Everything you learned in 1st grade is wrong.

A theorem:

x = y
(postulate)
x^2 = xy
(multiply both sides by x )
x^2 - y^2 = xy - y^2
(subtract y^2 from both sides )
(x+y) (x-y) = y(x-y)
(simple factoring )
x + y = y
(divide by (x - y) )
y + y = y
(as x = y (given postulate) , substitute)
2y = y
(y + y = 2y )

2 = 1
(divide by y )


2 equals 1.

Enough said.