已知xy^2=-2,求-xy(x^3y^7-3x^2y^5-y)的值

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已知xy^2=-2,求-xy(x^3y^7-3x^2y^5-y)的值
已知xy^2=-2,求-xy(x^3y^7-3x^2y^5-y)的值

已知xy^2=-2,求-xy(x^3y^7-3x^2y^5-y)的值
已知xy^2=-2
那么-xy(x^3y^7-3x^2y^5-y)
=-x^4y^8+3x^3y^6+xy^2
=-(-2)^4+3*(-2)^3+(-2)
=-16-24-2
=-42
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原式=-x^4y^8+3x^3y^6+xy^2
=-(xy^2)^4+3(xy^2)^3+xy^2
=-16-24-2
=-42

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