先化简,再求值(3x2y-2xy2)-(xy2-2x2y),其中x=-1,y=2.
(3x2y-2xy2)-(xy2-2x2y)
=3x2y-2xy2-xy2+2x2y
=5x2y-3xy2
当x=-1,y=2时,
原式=5×(-1)2×2-3×(-1)×22=10+12=22.
先化简,再求值(3x2y-2xy2)-(xy2-2x2y),其中x=-1,y=2.
(3x2y-2xy2)-(xy2-2x2y)
=3x2y-2xy2-xy2+2x2y
=5x2y-3xy2
当x=-1,y=2时,
原式=5×(-1)2×2-3×(-1)×22=10+12=22.