Question

求代數(shù)式3x2y-[2xy2-2(xy-

3

2

x2y)+xy]+3xy2的值，其中x=3，y=-

1

3

．

Answer 1

3x2y-[2xy2-2(xy-

3

2

x2y)+xy]+3xy2，
=3x²y-2xy²+2xy-3x²y-xy+3xy²，
=xy²+xy，
當(dāng)x=3，y=-

1

3

時，原式=3×

1

9

-1=-

2

3

．