a^2 - b^2 = ab-b^2
(a-b)(a+b) = b(a-b)

If you multiply out (distribute) the 2nd line, you get the first. For example:

(a-b)(a+b) = a^2 - -ba + ab - b^2 = a^2 - b^2

"Recollect me darlin, raise me to your lips, two undernourished egos, four rotating hips"

Inertia Creeps by Massive Attack