ĐKXĐ: `x > 4/25`
`(13x + 1) / \sqrt{25x - 4} + (13x - 1) / \sqrt{25 + 4x} = 20\sqrt{x}`
Chia `2` vế cho `\sqrt{x}` ta có
`(13x + 1) / \sqrt{25x^2 - 4x} + (13x - 1) / \sqrt{25x + 4x^2} = 20`
Với `x=1` thì
`14 / \sqrt{21} + 12 / \sqrt{29} = 20` (t/m)
Vỡi `x>1` thì
`(13x + 1) / \sqrt{25x^2 - 4x} > 14 / \sqrt{21}`
`(13x - 1) / \sqrt{25x + 4x^2} > 12 / \sqrt{29}`
`=> VT>VP`
Với `4/25<x<1` thì
`(13x + 1) / \sqrt{25x^2 - 4x} < 14 / \sqrt{21}`
`(13x - 1) / \sqrt{25x + 4x^2} < 12 / \sqrt{29}`
`=>VT<VP`
Vậy `x=1`