先化简再求值: (I) 求3x2y-[5xy2+2(x2y-
(II) 已知x,y,z满足:(1)已知|x-2|+(y+3)2=0,(2)z是最大的负整数,化简求值:2(x2y+xyz)-3(x2y-xyz)-4x2y. |
(1)原式=3x2y-5xy2-2x2y+1-x2y+6xy2=xy2+1,
当x=-2,y=
时,原式=-2×(1 2
)2+1=-1 2
+1=1 2
;1 2
(2)∵|x-2|+(y+3)2=0,z是最大的负整数,
∴x=2,y=-3,z=-1,
而原式=2x2y+2xyz-3x2y+3xyz-4x2y=5xyz-5x2y,
当x=2,y=-3,y=-1时,原式=5×2×(-3)×(-1)-5×22×(-3)=90.