已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值.
-xy(x^3y^7-3x^2y^5-y)
=-x^4y^8+3x^3y^6+xy^2
=-(xy^2)^4+3(xy^2)^3+xy^2
=-(-3)^4+3(-3)^3+(-3)^2
=-3^4-3^4+3^2
=-153