Question

先化简，再求值：3xy^2-2(xy^2-3/2x^2y)+(3xy^2y-2xy^2) 其中x=-4 y=1/2

3xy^2-2(xy^2-3/2x^2y)+(3xy^2y-2xy^2) 其中x=-4 y=1/2

Answer 1

这个题秒看不难：
解析：原式=3xy^2-2xy^2+3x^2y+3x^2y-2xy^2
=-xy^2+6x^2y
=xy(6x-y)
代入 x=-4 y=1/2
=49

Answer 2

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

=1/12