Question

How did it become from
l2+ 2lm + m2–4lm
to l2–2lm + m2
?

Answer 1

Answer:

l²+2lm+m²-4lm

l²+m²+2lm-4lm

l²+m²-4lm ( same quantity get cancel out and sign is of the greater one )

Answer 2

Answer:

=l

2

+2.l.m+m

2

−4lm

=l

2

+2lm+m

2

−4lm

\begin{gathered} = {l}^{2} - 2lm + {m}^{2} \\ \\ = {(l - m)}^{2} \\ \\ = (l - m)(l - m)\end{gathered}

=l

2

−2lm+m

2

=(l−m)

2

=(l−m)(l−m)