`C = \sqrt{2x + 4 + 6\sqrt{2x - 5}} + \sqrt{2x - 4 - 2\sqrt{2x - 5}} ( x ≥ 5/2)`
`C = \sqrt{2x - 5 + 6\sqrt{2x - 5} + 9 } + \sqrt{2x - 5 - 2\sqrt{2x - 5} + 1} `
`C = \sqrt{(\sqrt{2x - 5} + 3)^2 } + \sqrt{(\sqrt{2x - 5 - 1)^2} } `
`C = | \sqrt{2x - 5} + 3| + | \sqrt{2x - 5} - 1|`
`Với x ≥ 5/2`
`C = \sqrt{2x - 5} + 3 + | \sqrt{2x - 5} - 1|`
`Với \sqrt{2x - 5} - 1 ≥ 0`
`⇒ C = \sqrt{2x - 5} + 3 + \sqrt{2x - 5} - 1`
` C = 2\sqrt{2x - 5} + 2`
`Với \sqrt{2x - 5} - 1 ≤ 0`
`⇒ C = \sqrt{2x - 5} + 3 - \sqrt{2x - 5} + 1`
` C = 4` `(loại)`
`Vậy C = 2\sqrt{2x - 5} + 2`