1. Căn 6+căn 14 / 2 căn 3+căn 28
$\frac{√6+√14}{2√3 + √28 }$ =$\frac{√2 . (√3 . √7)}{2.(√3.√7)}$ = $\frac{√2}{2}$
2. 2 căn 2x - 5 căn 8x + 7 căn 18x = 28
đk: x>/0
(*) ⇔ 2√2x - 10√2x + 21√2x = 28
⇔ 13√2x = 28 ⇔√2x = $\frac{28}{13}$ ⇔ 2x = ($\frac{28}{13}$²⇔ x = $\frac{392}{169}$ (N)
Kl: x = $\frac{392}{169}$
4. Căn 5x-4 / căn x+2 =2
⇔ √5x-4 = 2√x+2
⇔ 5x-4 = 4x+8
⇔ x = 12