七年级数学分解因式4道！急！！！！

ax-ay - x平方+2xy -y 平方
=a(x-y)-(x-y)^2
=(a-x+y)(x-y)

x平方+xy -2y-4
=(x^2-4)+y(x-2)
=(x-2)(x+2+y)

x平方-4y平方-z平方+4yz,
=x^2-(2y-z)^2
=(x-2y+z)(x+2y-z)

4x平方-20xy+25y平方-9
=(2x-5y)^2-9
=(2x-5y-3)(2x-5y+3)

ax-ay - x平方+2xy -y 平方
=a(x-y)-(x-y)^2
=(x-y)(a-x+y)

x平方+xy -2y-4
=(x+2)(x-2)+y(x-2)
=(x-2)(x+y+2)

x平方-4y平方-z平方+4yz
=x^2-(4y^2+z^2-4yz)
=x^2-(2y-z)^2
=(x+2y-z)(x-2y+z)

4x平方-20xy+25y平方-9
=(2x-5y)^2-9
=((2x-5y+3)(2x-5y-3)

按顺序来：1.(a-x+y)(x-y)
2.(x-2)(x+y+2)
3.(x+2y-z)(x-2y+z)
4.(2x-5y+3)(2x-5y-3)

（x-y)(a-x+y)
(x+y+2)(x-2)