Question

factorise: -
(l+m) ² - 4lm

Answer 1

l^2 + m^2 + 2lm - 4lm 
l^2 + m^2 - 2lm 
(l-m)^2

Answer 2

hope u understand this one.
$(l {}^{2} + m {}^{2} + 2lm) - 4lm = l {}^{2} + m {}^{2} + 2lm - 4lm = l {}^{2} + m {}^{2} - 2lm = l {}^{2} + m {}^{2} - 2 \times l \times m = (l - m) { }^{2}$