2 = 1

How can 2 = 1 ?

First, recall

(a + b)(a – b)

= a2 – ab + ab – b2

= a2 – b2

Then let’s go:

a = b

a2 = ab

a2 – b2 = ab – b2

(a + b)(a – b) = b(a – b)

Cancel (a – b)

a + b = b

Remember a = b so

b + b = b

2b = b

2 = 1

What’s wrong?