ĐK : `x \ge 0`
`sqrt{(x-2sqrtx+1)/(x+2sqrtx+1)}`
`= (sqrt{x-2sqrtx+1})/(sqrt{x+2sqrtx+1})`
`= (sqrt{sqrtx^2-2sqrtx*1+1^2})/(sqrt{x^2+2sqrtx*1+1^2})`
`= (sqrt{(sqrtx-1)^2})/(sqrt{(sqrtx+1)^2})`
`= (sqrtx-1)/(sqrtx+1)`
`= ((sqrtx-1)^2)/((sqrtx+1)(sqrtx-1))`
`= (sqrtx^2-2sqrtx*1+1^2)/(sqrtx^2-1^2)`
`= (x-2sqrtx+1)/(x-1)`
