Question

3（x的2次方y+xy）-4（xy-2x的2次方y）-（-xy）化简

Answer 1

x^3y xy^3 2x^2y^3
=xy(x^2 y^2 2xy^2)
=xy[(x y)^2 2xy^2-2xy]
=xy[(x y)^2 2xy(y-1)]
=(3/4)[4 3(y-1)/2]
=3 9(y-1)/8
=15/8 9y/8

x y=2 xy=3/4
x,y是方程4x^2-8x 3=0的两根
(2x-1)(2x-3)=0
x1=1/2 x2=3/2
即y的取值为1/2或3/2,分别代入
15/8 9*(1/2)/8=39/16
15/8 9*(3/2)/8=57/16

Answer 2

原式=3x²y+3xy-4xy+8x²y+xy
=11x²y

Answer 3

3（x的2次方y+xy）-4（xy-2x的2次方y）-（-xy）
=3x²y+3xy-4xy+8x²y+xy
=11x²y

追问

2(x的2次方-x+1）-（-2x+3x的2次方）+（1-x）化简