Question

1.若x+(1/x)=3,求(x^2)/(x^4+x^2+1)的值是 ( )

Answer 1

1、x+1/x=(x^2+1)/x=3这是已知的

1/[x^2/(x^4+x^2+1)]=x^2+1/x^2+1

=(x+1/x)^2-1

=8

∴ x^2/(x^4+x^2+1)=1/8

选择A

2、(x+a)/(x-2)=-1

=>(2x+a-2)/(x-2)=0

=>x=1-a/2且x≠2

由题知根大于0则有a