9(m-n)平方-12m+12n+4
问题描述：
9(m-n)平方-12m+12n+4
答
9(m-n)^2-12m+12n+4
=[3(m-n)]^2-12(m-n)+4
=[3(m-n)]^2-2*3(m-n)*2+2^2
=[3(m-n)-2]^2
=(3m-3n-2)^2
^2是 平方