Question

Answer 1

\(=\left(m+n-m+n\right)\left(m+n+m-n\right)=2m\cdot2n=4mn\)

Answer 2

\(\left(m+n\right)^2-\left(m-n\right)^2=\left(m+n-m+n\right)\left(m+n+m-n\right)=2n.2m=4mn\)

Answer 3

\(=\left(m+n+m-n\right)\left(m+n-m+n\right)\)

=4mn

Answer 4

`(m+n-m+n)(m+n+m-n)`

`= 4mn`