化简求职:2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y其中x=-2/3,y=-1/2
问题描述:
化简求职:2xy^2-[3xy^2-2(x^2y-(1/2)xy^2)]-2x^2y其中x=-2/3,y=-1/2
答
2xy²-[3xy²-2(x²y-(1/2)xy²)]-2x²y
=(2-3)xy²+2x²y+(1/2)xy²-2x²y
=(1/2)xy²-xy²
=-(1/2)xy²
x=-2/3,y=-1/2
带入,得
-(1/2)×-2/3×(-1/2)²
=1/122(x²y-(1/2)xy²的2x²y+(1/2)xy²不应该是+xy吗,乘以2奥2xy²-[3xy²-2(x²y-(1/2)xy²)]-2x²y=(2-3)xy²+2x²y-2×(1/2)xy²-2x²y=-xy²-xy²=-2xy²x=-2/3,y=-1/2带入,得-2×(-2/3)×(-1/2)²=1/3