a = 1
b = 1

a = b
a(a) = ab [multiply both sides by a]

a(a) - b(b) = ab-b(b) [subtract both sides by b(b)]

(a+b)(a-b) = b(a-b) [factorise them]
(a+b)(a-b)/(a-b) = b(a-b)/(a-b) [divide by a-b]
a+b = b

Recalling back a=1 b=1

a+b=b

1 + 1 = 1

1 + 1 = 1 What went wrong?

Another one

-2 = -2
4 - 6 = 1 - 3
4 - 6 + 9/4 = 1 - 3 + 9/4
(2 - 3/2) square = (1 - 3/2) square

2 - 3/2 = 1 - 3/2
2 = 1

credits to kenneth