Question

factorise the following

Answer 1

Given (l + m)^2 - 4lm

We know that (a + b)^2 = a^2 + b^2 + 2ab

Then (l + m)^2 = l^2 + m^2 + 2lm

                         = l^2  + m^2 + 2lm - 4lm

                        =  l^2 + m^2 - 2lm

                       = (l - m)^2.


Hope this helps!

Answer 2

$(l + m) ^{2} - 4lm \\ l ^{2} + m ^{2} - 4lm \\ l ^{2} + m^{2} - 2lm \\ (l -m) ^{2} \\ = (l - m)( l- m)$