因式分解：25(x+y)²-9(x-y)²；（x+y）²-4（x+y-1）.

因式分解：25(x+y)²-9(x-y)²；（x+y）²-4（x+y-1）.
因式分解：25(x+y)²-9(x-y)²；（x+y）²-4（x+y-1）.

因式分解：25(x+y)²-9(x-y)²；（x+y）²-4（x+y-1）.
25(x+y)²-9(x-y)²
=[5(x+y)-3(x-y)][5(x+y)+3(x-y)]
=(2x+8y)(8x+2y)
=4(x+4y)(4x+y)

（x+y）²-4（x+y-1）.
=（x+y）²-4（x+y)+4
=(x+y-2)^2