Question

Factorise the following expression.

(l + m)² − 4lm (Hint: Expand (l + m)² first)

Answer 1

(l + m)² − 4lm

 = l² + 2 × l × m + m² − 4lm      ...[∵ (a + b)² = a² + 2ab + b²]

= l² − 2lm + m² − 4lm

= l² − 2lm + m²

= (l − m)²

= (l − m) (l − m)