concepto de multiplicacion de binomios
(a + b) . (x + y) =
= a . (x + y) + b . (x + y )
= ax + ay + bx + by
–
(a + b) . (a – b) =
= a . (a – b) + b . (a – b)
= aa – ab + ba – bb
= a2 - ab + ab – b2
= a2 – b2