“Proof”. Let a = b.
a2 = ab (Multiply both sides by a.)
a2 +a2 2ab=ab+a2 2ab(Adda2 2abtobothsides.)
2(a2  ab) = a2  ab (Factor the left, and collect like terms on the right.)
2 = 1 (Divide both sides by a2  ab.)