解：利用平方差公式：a²-b²=(a+b)(a-b) 4(x+y)²-9(x-y)²=[2(x+y)]²-[3(x-y)]²=[2(x+y)+3(x-y)][2(x+y)-3(x-y)]=(5x-y)(-x+5y)
[2(x+y)+3(x-y)][2(x+y)-3(x-y)]=(5x-y)(5y-x)
(2x+2y+3x-3y)(2x+2y-3x+3y)=(5x-y)(-x+5y)
