(2x3-3x2y-2xy2)-(x3-2xy2+y3)+(-x3+3x2y-y3)当x=1/2,y=-1时,求值.当x=-1/2,y=-1时,求值.
问题描述:
(2x3-3x2y-2xy2)-(x3-2xy2+y3)+(-x3+3x2y-y3)
当x=1/2,y=-1时,求值.当x=-1/2,y=-1时,求值.
答
(2x3-3x2y-2xy2)-(x3-2xy2+y3)+(-x3+3x2y-y3) =2x3-3x2y-2xy2-x3+2xy2-y3-x3+3x2y-y3 = -2y3 当x=1/2,y=-1时,原式=-2y3=-2*(-1)=2 当x=-1/2,y=-1时,原式=-2y3=-2*(-1)=2