Question

Factorise.

(l + m)² − (l − m)²

Answer 1

(l + m)² − (l − m)²

Using the identity a² − b² = (a − b) (a + b)

= [(l + m) + (l − m)] [(l + m) − ( l − m)]

= (l + m + l − m) (l + m − l + m)

= (2 m) (2 l)

= 4 lm