Factorise the following expression:
(l+m)2 - 4lm
We have
(l + m)2 - 4lm = (l2 + 2lm + m2) - 4lm
[ Collecting the like terms 2lm and -4lm]
= l2 + (2lm - 4lm) + m2
= l2 + 2lm + m2
=
=
∴