已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值第二步=-(xy^2)^4+3(xy^2)^3+(xy^2)

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已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值第二步=-(xy^2)^4+3(xy^2)^3+(xy^2)
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已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值第二步=-(xy^2)^4+3(xy^2)^3+(xy^2)
已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值
第二步
=-(xy^2)^4+3(xy^2)^3+(xy^2)

已知xy^2=-3,求-xy(x^3y^7-3x^2y^5-y)的值第二步=-(xy^2)^4+3(xy^2)^3+(xy^2)
楼主算得对,第一个回答在第二步的地方把三次方的系数 3 弄丢掉了,所以正确的还是-165

-xy(x^3y^7-3x^2y^5-y)
=-x^4y^8+3x^3y^6+xy^2
=-(xy^2)^4+(xy^2)^3+(xy^2)
=-(-3)^4+(-3)^3+(-3)
=-81-27-3
=-111

原式=-x^4y^8+3x^3y^6+xy^2
=-(xy^2)^4+3(xy^2)^3+xy^2
当xy^2=-3时，原式=-（-3）^4+3(-3)^3+(-3)
=(-81）+(-81)+(-3)
=(-3)

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