Question

(5)先化简,再求值:3x2y-[2x2y-(2xy-3x2y)]+3xy2,其中x=3,y=-1/3

(5)先化简，再求值：3x2y－[2x2y－(2xy－3x2y)]＋3xy2，其中x＝3，y＝1/3

Answer 1

3x^2y－[2x^2y－(2xy－3x^2y)]＋3xy^2
=3x^2y－[2x^2y－2xy+3x^2y]＋3xy^2
=3x^2y－5x^2y+2xy＋3xy^2
=-2x^2y+2xy＋3xy^2
=-2*3^2*(-1/3)+2*3*(-1/3)+3*3*(-1/3)^2
=6-2+1
=5

Answer 2

数理答疑团为您解答，希望对你有所帮助。

3x2y－[2x2y－(2xy－3x2y)]＋3xy2
=3x²y-[2x²y-2xy+3x²y]+3xy²
=3x²y-5x²y+2xy+3xy²
=-2x²y+2xy+3xy²
=xy(-2x+2+3y)

当x=3,y=1/3时
原式= 1*(-6 + 2 +1）= -3

祝你学习进步，更上一层楼！ (*^__^*)

Answer 3

3x2y－[2x2y－(2xy－3x2y)]＋3xy2

=3x²y-[2x²y-2xy+3x²y]+3xy²
=3x²y-5x²y+2xy+3xy²
=-2x²y+2xy+3xy²
x=3,y=-1/3时
原式=-2×2²×(-1/3)+2×3×(-1/3)+3×3×(-1/3)²
=5/3

Answer 4

3x2y－[2x2y－(2xy－3x2y)]＋3xy2
=3x²y-2x²y+2xy-3x²y+3xy²
=-2x²y+2xy+3xy²
=-6+2+1
=-3 y=1/3? 还是-1/3 我算的是1/3