Let a and b each be equal to 1.
Since a and b are equal,
b2 = ab (eq 1)
It is obvious that a2 = a2 (eq 2)
Subtract equation 1 from equation 2, we have
a2 – b2 = a2 – ab (eq 3)
Factor both sides, we have
(a + b)(a – b) = a(a-b) (eq 4)
Next, divide both sides of the equation 4 by (a – b) and we get
a + b = a (eq 5)
Since we set a and b both equal to 1 at the beginning of this proof, so this means
1 + 1 = 1
Therefore, 1 = 2
QED.