ĐKXĐ : `x \ne 1 , x > 0`
`P = (xsqrtx-1)/(x-sqrtx)-(xsqrtx+1)/(x+sqrtx)+(x+1)/(sqrtx)`
`= ((sqrtx-1)(x+sqrtx+1))/(sqrtx(sqrtx-1)) - ((sqrtx+1)(x-sqrtx+1))/(sqrtx(sqrtx+1)) + (x+1)/sqrtx`
`= (x+sqrtx+1)/sqrtx - (x-sqrtx+1)/sqrtx + (x+1)/sqrtx`
`= (x+sqrtx+1-(x-sqrtx+1)+x+1)/sqrtx`
`= (x+sqrtx+1-x+sqrtx-1+x+1)/sqrtx`
`= (2sqrtx+x+1)/(sqrtx)`
..........................................................
`P = 9/2`
`⇔ (2sqrtx+x+1)/sqrtx = 9/2`
`⇔ 2(2sqrtx+x+1) = 9sqrtx`
`⇔ 4sqrtx + 2x + 2 = 9sqrtx`
`⇔ 4sqrtx - 9sqrtx = -2x - 2`
`⇔ -5sqrtx = -2x-2`
`⇔ (-5sqrtx)^2 = (-2x-2)^2`
`⇔ 25x = 4x^2 + 8x + 4`
`⇔ 25x - 4x^2 - 8x - 4 = 0`
`⇔ 4x^2 - 17x + 4 = 0`
`\Detlta = (-17)^2-4*4*4 = 225`
Vây pt có 2 nghiệm pb :
`x_1 = (-(-17)+sqrt{225})/(2*4) = 4(TM)`
`x_2 =(-(-17)-sqrt{225})/(2*4) = 1/4(TM)`
