1、6q(p+q)-4p(p+q)
=2(p+q)(3q-2p)
2、x(x-y)^2-y(x-y)^2
=(x-y)^2(x-y)
=(x-y)^3
3、x(x+y)(x-y)-x(x+y)^2
=x(x+y)[x-y-(x+y)]
=-2xy(x+y)