Question

化简求值2(x^2+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1

2x^3+4x-1/3x^2-(x+3x^2-2x^3),其中x=-3

Answer 1

2(x^2+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1
=2x²+2xy-3x²y+3xy-4x²y
=2x²+5xy-7x²y
=2*1²+5*1*(-1)-7*1²*(-1)
=2-5+7
=4

2x^3+4x-1/3x^2-(x+3x^2-2x^3),其中x=-3
=2x³+4x-1/3x²-x-3x²+2x³
=4x³+3x-10/3x²
=4*(-3)³+3*(-3)-10/3*(-3)²
=4*(-27)-9-10/3*9
=-108-9-30
=-147

追问

2(x^2y+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1呢？

追答

2(x^2+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1
=2x²+2xy-3x²y+3xy-4x²y
=2x²+5xy-7x²y
=2*1²+5*1*(-1)-7*1²*(-1)
=2-5+7
=4

追问

是2(x^2y+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1啊！多了个y

追答

2(x^2y+xy)-3(x^2y-xy)-4x^2y
=2x²y+2xy-3x²y+3xy-4x²y
=5xy-5x²y
=5xy(1-x)
=5*1*(-1)(1-1)
=0

Answer 2

1. 原式=2x^2+2xy-3x^2y+3xy-4x^2y=2x^2+5xy-7x^2y=x(2x+5y-7xy)=1×[2×1+5×（-1）-7×1×（-1）]=[2-5+7]=4

追问

2(x^2y+xy)-3(x^2y-xy)-4x^2y其中x=1,y=-1呢？还有2x^3+4x-1/3x^2-(x+3x^2-2x^3),其中x=-3