16(x+y)²-25(x-y)²=[4(x+y)+5(x-y)] [4(x+y)-5(x-y)]=（9x-y）(-x+9y)希望我的解答能帮助您，不当之处欢迎继续追问
16(x+y)^2-25(x-y)^2=(4x+4y+5x-5y)(4x+4y-5x+5y)=(9x-y)(9y-x)
把式子化成[4（x+y)]^2-[5(x-y)]^2再按平方差公式分解
