4×(3x+2y)的2次－9(x-y)的2次
=4×(3x+2y)^2－9(x-y)^2
=[2(3x+2y)]^2-[3(x-y)]^2
=(6x+4y)^2-(3x-3y)^2
=(6x+4y+3x-3y)(6x+4y-3x+3y)
=(9x+y)(3x+7y)