1.已知y/x=3,求x+y/x-y2.已知X=根号3+1,y=根号3-1,求XX-YY/XXY+XYY3.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

Question

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

Answer 1

(x+y)/(x-y)
= (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