4(2x+y)的2次方-9(x-2y)的2次方
=【2（2X+Y)】^2-[(3(X-2Y)]^2
=[2(2X+Y)+3(X-2Y)][2(2X+Y)-3(X-2Y)]
=(4X+2Y+3X-6Y)(4X+2Y-3X+6Y)
=(7X-4Y)(X+8Y)