四道分解因式：1.(x+y)²-4（x+y-1) 2.(x²+y²)²-4x²y²3.(x²-2x)²+2(x²-2x)+1 4.(x+y)²-6x²+6y²+9(x-y)²

四道分解因式：1.(x+y)²-4（x+y-1) 2.(x²+y²)²-4x²y²3.(x²-2x)²+2(x²-2x)+1 4.(x+y)²-6x²+6y²+9(x-y)²
四道分解因式：1.(x+y)²-4（x+y-1) 2.(x²+y²)²-4x²y²
3.(x²-2x)²+2(x²-2x)+1 4.(x+y)²-6x²+6y²+9(x-y)²

四道分解因式：1.(x+y)²-4（x+y-1) 2.(x²+y²)²-4x²y²3.(x²-2x)²+2(x²-2x)+1 4.(x+y)²-6x²+6y²+9(x-y)²
1.(x+y)²-4（x+y-1)
=(x+y)²-4(x+y)+4
=(x+y-2)²
2.(x²+y²)²-4x²y²
=(x²+y²+2xy)(x²+y²-2xy)
=(x+y)²(x-y)²
3.(x²-2x)²+2(x²-2x)+1
=(x²-2x+1)²
=(x-1)⁴
4.(x+y)²-6x²+6y²+9(x-y)²
=(x+y)²-6(x²-y²)+[3(x-y)]²
=[(x+y)-3(x-y)]²
=(x+y-3x+3y)²
=(-2x+4y)²
=4(x-2y)²