已知xy^2=-2求xy（2x^3y^7+5x^2y^5-y)的值_数学解答

已知xy^2=-2求xy（2x^3y^7+5x^2y^5-y)的值

人气：168 ℃　时间：2019-10-18 02:30:35

解答

xy（2x^3y^7+5x^2y^5-y)
=xy[2y(xy^2)^3+5y(xy^2)^2-y]
=xy[2y(-2)^3+5y(-2)^2-y]
=xy(-16y+20y-y)
=3xy^2
=3*(-2)
=-6