Question

Find $(l+m{)}^2-(l-m{)}^2$.

• A. $4lm$
• B. $2lm$
• C. $0$
• D. $1$

Answer 1

The correct option is A $4lm$

we can use the identity $(a^2-b^2)=(a+b)(a-b)$

$i.e(l+m+l-m)(l+m-l+m)=2l\times 2m=4lm$