分解因式,2(m-n)^2-8m^2
要过程,越详细越好
=2m^2-4mn+2n^2-8m^2
=-6m^2-4mn+2n^2
=-2(3m^2+2mn-n^2)
= -2(m+n)(3m-n)用十字相乘法!!!