Giải bài 4 trang 40

Đề bài

Tìm x, biết:

a) $\sqrt{x}=9$

b) $\sqrt{x}=\sqrt{5}$

c) $3\sqrt{x}=1$

d) $2\sqrt{x+1}=12$

Lời giải chi tiết

a) $\sqrt{x}=9$

$\begin{array}{c}{\left(\sqrt{x}\right)}^2={\left(9\right)}^2\\ x=81\end{array}$

b) $\sqrt{x}=\sqrt{5}$

$\begin{array}{c}{\left(\sqrt{x}\right)}^2={\left(\sqrt{5}\right)}^2\\ x=5\end{array}$

c) $3\sqrt{x}=1$

$\begin{array}{c}{\left(\sqrt{x}\right)}^2={\left(\frac{1}{3}\right)}^2\\ x=\frac{1}{9}\end{array}$

d) $2\sqrt{x+1}=12$

$\begin{array}{c}\sqrt{x+1}=6\\ {\left(\sqrt{x+1}\right)}^2=6^2\\ x+1=36\\ x=35\end{array}$