1) $\sqrt{x}$ = 4
(=) x = 4²
(=) x = 16
Vậy S = 16
2) $\sqrt{x+3}$ = l-5l
(=) $\sqrt{x+3}$ = 5
(=) $\sqrt{x+3}$ = 5²
(=) x+3 = 25
(=) x = 22
Vậy S = 22
3) $\sqrt{4x+4}$ + $\sqrt{9x+9}$ = 12 - $\sqrt{x+1}$
(=) $\sqrt{4(x+1)}$ + $\sqrt{9(x+1)}$ = 12 - $\sqrt{x+1}$
(=) 2$\sqrt{x+1}$ + 3$\sqrt{x+1}$ = 12 - $\sqrt{x+1}$
(=) 5$\sqrt{x+1}$ = 12 - $\sqrt{x+1}$
(=) 5$\sqrt{x+1}$ + $\sqrt{x+1}$ = 12
(=) 6$\sqrt{x+1}$ =12
(=) $\sqrt{x+1}$ =2
(=) x+1=4
(=) x = 3
Vậy S = 3
4) $\sqrt{25x-25}$ - $\sqrt{16x-16}$ + $\sqrt{4x-4}$ = 6
(=) $\sqrt{25(x-1)}$ - $\sqrt{16(x-1)}$ + $\sqrt{4(x-1)}$ = 6
(=) 5$\sqrt{x-1}$ - 4$\sqrt{x-1}$ + 2$\sqrt{x-1}$ = 6
(=) 3$\sqrt{x-1}$ = 6
(=) $\sqrt{x-1}$ = 2
(=) x-1=2²
(=) x-1 = 4
(=) x=5
Vậy S =5
