Question

9(m+n)的2次方-（m-n）的2次方

Answer 1

9(m+n)^2-(m-n)^2
=[3(m+n)-(m-n)][3(m+n)+(m-n)]
=(3m+3n-m+n)(3m+3n+m-n)
=(2m+4n)(4m+2n)
=4(m+2n)(2m+n)

追问

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

怎么变的

追答

=(2m+4n)(4m+2n)
=[2*(m+2n)][2*(2m+n)]
=2*2*(m+2n)(2m+n)
=4(m+2n)(2m+n)