1.已知y/x=3，求x+y/x-y 2.已知X=根号3+1，y=根号3-1，求XX-YY/XXY+XYY
3.若Y=XX/2-3X,X取何值时（1）Y=正数（2）Y=负数（3）Y=0（4）分式无意义
4.已知XX+5X+1=0.求XX+1/XX
加急 五分钟内要
= (x/x+y/x)/(x/x-y/x)
= (1+y/x)/(1-y/x)
=(1-3)/(1+3)
=-2/4
=-1/2
x=√3+1,y=√3-1
(x^2-y^2)/(x^2y+xy^2)
=(x+y)(x-y)/[xy(x+y)]
=(x-y)/(xy)
=(√3+1-√3+1)/(√3+1)(√3-1)
=2/2
=1
Y为正数
y=x^2/(2-3x)
x^2/(2-3x)>0
(2-3x)>0
x<2/3
Y为负数
x^2/(2-3x)<0
(2-3x)<0
x>2/3
Y=0
x^2=0
x=0
分式无意义
2-3x=0
x=2/3
x^2+5x+1=0
x+5+1/x=0
x+1/x=-5
x^2+1/x^2
=(x+1/x)^2-2
=(-5)^2-2
=25-2
=23
(x+y)/(x-y)=4x/(-2x)=-2
2:(x²-y²)/(x²y+xy²)
=(x-y)/(xy)
=2/2
=1
3:y=x²/（2-3x）
(1)x²/（2-3x）>0
x²>0且2-3x>0 或 x²<0且2-3x<0
x<2/3且x不等于0
(2)x²/(2-3x)<0
x²>0且2-3x<0 或 x²<0且2-3x>0
x>2/3
(3)x²/(2-3x)=0
x²=0且2-3x不等于0
x=0
(4) 2-3x=0
x=2/3
4:x²+5x+1=0 两边除以x
x+5+1/x=0
x+1/x=-5
x²+1/x²=(x+1/x)²-2=25-2=23
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