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Proof that 2 = 1

let a = b
a� = ab
Multiply both sides by a
a� + a� - 2ab = ab + a� - 2ab
Add (a� - 2ab) to both sides
2(a� - ab) = a� - ab
Factor the left, and collect like terms on the right
2 = 1
Divide both sides by (a� - ab)

This proof can also be used as a proof by contradiction that a can never be equal to b.

Related pages in this website

Index of joke proofs

An alternative proof that 2=1

A proof by induction that e = π

The webmaster and author of this Math Help site is Graeme McRae.