第一题：(x-2y)*x^3-(y-2x)*y^3=x^4-2x^3y-y^4+2xy^3=(x^4-y^4)-2xy(x^2-y^2)=(x^2+y^2-2xy)(x^2-y^2)
=(x-y)^2*(x+y)*(x-y)=(x-y)^3*(x+y)
第二题看不懂……