A = B
A^{2} = AB
A^{2}  B^{2}
= AB  B^{2}
(A + B)(A  B) = B(A  B)
A + B = B
B + B = B
1 + 1 = 1
2 = 1

No reason, just letting A = B.
Multiplying both sides by A.
Subtracting B^{2}
from both sides.
Factoring both sides.
Dividing both sides by A  B
Substituting A = B
Dividing both sides by B.
Double Integrity
