Question

分解因式(m-n)^2-9(m +n)^2

Answer 1

(m-n)^2-9(m +n)^2=(m-n)^2-[3(m +n)]^2

=[(m-n)+3(m +n)][(m-n)-3(m +n)]

=(4m+2n)(-2m-4n)

=-4(2m+n)(m+2n).