ĐKXĐ : `x \ge 0`
`sqrtx + 2sqrtx - 1 = x`
`⇔ 3sqrtx = x + 1`
`⇔ (3sqrtx)^2 = (x+1)^2`
`⇔ 9x = x^2 + 2x + 1`
`⇔ x^2 - 7x + 1 = 0`
`\Delta = (-7)^2 - 4 * 1 * 4 = 45`
Vì `\Delta > 0 ⇒` pt có 2 nghiệm pb :
`x_1 = (-(-7)+sqrt{45})/(2*1) = (7+3sqrt5)/2(TMĐK)`
`x_2 = (-(-7)-sqrt{45})/(2*1) = (7-3sqrt5)/2 (TMĐK)`
Vậy `S = {(7+3sqrt5)/2,(7-3sqrt5)/2}`
___________________________
ĐKXĐ : `x \ge 0`
`sqrtx + 2sqrtx - 1 = 2`
`⇔ 3sqrtx = 2 + 1`
`⇔ sqrtx = 1`
`⇔ x = 1(TMĐK)`
Vậy `S = {1}`
