(x+y)(5m+3n)²-(x+y)(m-n)²
=(x+y)[(5m+3n)²-(m-n)²]
=(x+y)[(5m+3n)+(m-n)][(5m+3n)-(m-n)]
=(x+y)(6m+2n)(4m+4n)
=8(x+y)(3m+n)(m+n)为什么是8(x+y)(3m+n)(m+n） 我不明白咋从 (x+y)(6m+2n)(4m+4n)提取公因数。2*4=8