Đáp án:
`C=1/(2\sqrtx-2)-1/(2\sqrtx+2)+\sqrtx/(1-x)`
Điều kiện:`x>=0,x ne 1`
`C=1/(2(\sqrtx-1))-1/(2(\sqrtx+1))-\sqrtx/(x-1)`
`C=(\sqrtx+1-(\sqrtx-1)-2\sqrtx)/(2(\sqrtx-1)(\sqrtx+1))`
`C=(2-2\sqrtx)/(2(\sqrtx-1)(\sqrtx+1))`
`C=(2(1-\sqrtx))/(2(\sqrtx-1)(\sqrtx+1))`
`C=-1/(\sqrtx+1)`
`b)x=4/9`
`=>\sqrtx=2/3`
`=>C=(-1)/(2/3+1)`
`=(-1)/(5/3)=-3/5`
Vậy với `x=4/9` thì `C=-3/5.`
`c)|C|=1/3`
`<=>|(-1)/(\sqrtx+1)|=1/3`
`<=>1/(\sqrtx+1)=1/3`
`<=>\sqrtx+1=3`
`<=>\sqrtx=2`
`<=>x=4(tmđk)`
Vậy `x=4` thì `|C|=1/3`.
