Question

已知xy平方=-2,求-xy(x^3y^7-3x^3y^7-y)

Answer 1

-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

=-(-2)^4+3*(-2)^3-2

=-16-24-2

=-42