Bài `2:`

`1) sqrt{ (x+3)/(5 - x)}` 

ĐK : `(x + 3)/(5 - x) \ge 0`

TH1 : `{(x + 3 \ge 0),(5 - x > 0):} to -3 \le x < 5` (tm)

TH2 : `{(x +3\le0),(5-x<0):} to {(x\le -3),(x > 5):}` (ktm)

`2) sqrt{ (x-3)/(2 - x)}`

ĐK : `(x - 3)/(2 - x) \ge 0`

TH1: `{(x-3 \ge 0),(2-x> 0):} to {(x \ge 3),(x < 2):}` (ktm)

TH2 : `{(x-3\le0),(2-x<0):} to {(x\le3),(x > 2) to 2 < x \le 3` (tm)

`3) sqrt{ (x +2)/(2-x)}`

ĐK : `(x + 2)/(2 - x) \ge 0`

TH1 : `{(x+2\ge0),(2-x>0):} to {(x\ge-2),(x<2):} to -2\le x< 2` (tm)

TH2 : `{(x+2\le0),(2-x<0):} to {(x\le-2),(x>2):}` (ktm)

`4) (sqrt{x-3})/(sqrt{x+3})`

ĐK : `{(x-3\ge0),(x+3>0):} to {(x \ge 3),(x> -3):} to x \ge 3`

`5) (sqrt{2x+1})/(sqrt{x-4})`

ĐK : `{(2x+1\ge0),(x-4>0):} to {(x \ge -1/2),(x>4):} to x > 4`

`6) (sqrt{2x-4})/(sqrt{x+3})`

ĐK : `{(2x-4\ge0),(x+3>0):} to {(x\ge2),(x> -3):} to x \ge 2`

`7) sqrt{x^2 - 3x + 2}`

ĐK : `x^2 - 3x + 2 \ge 0`

`to (x - 1)(x - 2) \ge 0`

TH1 : `{(x-1\ge0),(x-2\ge0):} to {(x\ge1),(x\ge2):} to x \ge 2`

TH2 : `{(x-1\le0),(x-2\le0):}to {(x\le1),(x\le2):} to x \le 1`

`8) sqrt{x^2 + 4x + 5}`

ĐK : `x^2 + 4x + 5 \ge 0`

`to (x^2 + 4x + 4) + 1 \ge 0`

`to (x + 2)^2 + 1 \ge 0` (Luôn đúng)

`9) sqrt{9x^2 - 6x + 1}`

ĐK :`9x^2 - 6x + 1 \ge 0`

`to (3x)^2-2.3x.1+1^2\ge0`

`to(3x-1)^2 \ge 0` (Luôn đúng)