解分因式(x+y)(x-y)-(x+y)^2
=(x+y)(x-y-x-y)
=-2y(x+y)
(x+y)^2+mx+my
=(x+y)^2+m(x+y)
=(x+y)(x+y+m)
a(x-a)(x+y)^2-b(x-a)^2(x+y)
= (x-a)(x+y)(a(x+y)-b(x-a))
= (x-a)(x+y)(ax+ay-bx+ab)
a^3-a
=a(a^2-1)
=a(a-1)(a+1)
a^2-49b^2
=(a+7b)(a-7b)
9(x-y)^2-4(x+y)^2
=(3(x-y)+2(x+y))(3(x-y)-2(x+y))
=(3x-3y+2x+2y)(3x-3y-2x-2y)
=(5x-y)(x-5y)