16（3x+y)^2-9(3x-y)^2

因为16（3x+y)^2-9(3x-y)^2
=[4(3x+y)]^2-[3(3x-y)]^2
=[4(3x+y)+3(3x-y)][4(3x+y)-3(3x-y)]
=(12x+4y+9x-3y)(12x+4y-9x+3y)
=(21x+y)(3x+7y)

=[4(3x+y)-3(3x-y)][4(3x+y)+3(3x-y)]
=(12x+y-9x+y)(12x+4y+9x+3y)
=(21x+2y)(21x+7y)
剩下的自己解开吧
这是个简单的初中数学啊

16（3x+y)^2-9(3x-y)^2
=[4(3x+y)-3(3x-y)][4(3x+y)+3(3x-y)]
=(12x+4y-9x+3y)(12x+4y+9x-3y)
=(3x+7y)(21x+y)