2 câu trả lời
`3``\sqrt{x+1}` `= 40`
$\Rightarrow$ `3 . (x +1) = 40^{2}`
$\Rightarrow$ `9 . (x +1) = 1600`
$\Rightarrow$ `(x +1) = 1600 : 9`
$\Rightarrow$ `x +1 = 1600/9`
$\Rightarrow$ `x = 1600/9 - 1`
$\Rightarrow$ `x = 1600/9 - 9/9`
$\Rightarrow$ `x = {1600 - 9}/9`
$\Rightarrow$ `x = 1591/9`
$\text{Vậy}$ `x = 1591/9`
