9 9 x+ - =3 y + - =3 y z 9 则z+ - x

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9 9 x+ - =3 y + - =3 y z 9 则z+ - x
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9 9 x+ - =3 y + - =3 y z 9 则z+ - x
9 9 x+ - =3 y + - =3 y z 9 则z+ - x

9 9 x+ - =3 y + - =3 y z 9 则z+ - x
A交B为空
则联立方程组的解集为空,解此方程组
(y-3)/(x-2)=a+1
y=(a+1)x-2a+1
代入(a^2-1)x+(a-1)y=9
(a^2-1)x+(a-1)((a+1)x-2a+1)=9
(a^2-1)x+(a^2-1)x=(a-1)(2a-1)+9
则a^2-1=0
且(a-1)(2a-1)+9不为0
a=1或a=-1
或x=2
2a^2+3a-14=0
a=-3.5,或a=2
所以a的取值范围为(a|a=1,a=-1,a=2,a=-3.5)

3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 求函数f（x,y）=x×x×x－y×y×y+3×x×x+3×y×y－9x的极值 9y=3x-(x-1),4(x+y)-(2x+4)=8y 5x=3y,(2x+y)的平方=5x(x+y)+9 3x-2y=9 x-3y=2 x+y=5 x+2y=3 y=x 2x+y=8 3y=2x y/3=x/2 12/x=9/y y/x=?y/x=?x/y=? 根据3（x+y)-2(x-y)=11,4(x+y)+3(x-y)=9可得出x+y= ,x-y= 已知2x-y/x+2y=3,求2(2x-y)/x+2y-9(x+2y)/2x-y+3的值. x-y=3,xy=9,x+y=? Y=x+3 7x+5y=9 y-x=3 7x+5y=-9 y=x+3 7x+5y=9 2x+3y=9 x+y=20 {y=x+3,7x+5y+9; (x+3y)(_____)=9y^2 -x^2. （3x-y)·（)=9x²-y² （-2x-y+9)dy=(-y+x+3)dx