Question

有一道题"计算2(x^3-xy^2)-(x^3+3x^2y-2xy^2+y^3)+(3x^2y-x^3-y^3)的值

Answer 1

2(x^3-xy^2)-(x^3+3x^2y-2xy^2+y^3)+(3x^2y-x^3-y^3)

=2x^3-2xy^2-x^3-3x^2y+2xy^2-y^3+3x^2y-x^3-y^3

=-2y^3

当y=-1时,原式=-2×（-1）=2

因为最后结果与x无关,所以把x看成谁都不会影响结果.