Question

已知(3x+1)(3x-3)-3x+2)^2=-7,(y+7)(y-7)-y(y-7)=0,求8y^2-5y(-y+3x)+4y(-4y-5/2x)的值

Answer 1

(3x+1)(3x-3)-(3x+2)^2
=9x^2-6x-3-(9x^2+12x+4)
=-18x-7=-7
∴ x=0

(y+7)(y-7)-y(y-7)
=y^2-49-y^2+7y
=7y-49=0
∴ y=7

8y^2-5y(-y+3x)+4y(-4y-5/2x)
=8y^2+5y^2-15xy-16y^2-10xy
=-3y^2-25xy
=-3*7*7-0
=-147

Answer 2

(3x+1)(3x-3)-(3x+2)^2=-7
9x^2-6x-3-9x^2-12x-4=-7
-18x=0
x=0
(y+7)(y-7)-y(y-7)=0
y^2-49-y^2+7y=0
7y=49
y=7
8y^2-5y(-y+3x)+4y(-4y-5/2x)
=8y^2+5y^2-16y^2
=-3y^2
=-3x49
=-147

Answer 3

(3x+1)(3x-3)-(3x+2)^2=-7
9x^2-6x-3-9x^2-12x-4=-7
-18x-7=-7
18x=0
x=0

(y+7)(y-7)-y(y-7)=0,
y^2-49-y^2+7y=0
7y=49
y=7

8y^2-5y(-y+3x)+4y(-4y-5/2x)
=8y^2+5y^2-15xy-16y^2-10xy
=-3y^2-25xy
=-3x7^2
=-147

Answer 4

解得x=0,y=7
将原式代入x=0进行化简
原式=-3y^2=-147

有不明白的地方再问哟，祝你学习进步，更上一层楼！ (*^__^*)

Answer 5

缺半个括弧，没法算

追问

这你都看出来了还算不出

Answer 6

把x=0 y=7带入就可以了

Answer 7

(3x+1)(3x-3)-3x+2)^2=-7 这个写错了吧