已知xy2=-2,求(x2y5-2xy3-y)(-3xy)的值.
问题描述:
已知xy2=-2,求(x2y5-2xy3-y)(-3xy)的值.
答
原式=-3x3y6+6x2y4+3xy2,
当xy2=-2时,原式=-3(xy2)3+6(xy2)2+3×(-2)=-3×(-2)3+6×(-2)2-6=24+24-6=42.