Câu a:
\(\sqrt x = 15 \Leftrightarrow \left\{ \matrix{ x \ge 0 \hfill \cr {\left( {\sqrt x } \right)^2} = {\left( {15} \right)^2} \hfill \cr} \right. \) \(\Leftrightarrow x = 225\)
Câu b:
\(2\sqrt x = 14 \Leftrightarrow \left\{ \matrix{ x \ge 0 \hfill \cr \sqrt x = 14:2 \hfill \cr} \right.\)
\( \Leftrightarrow \left\{ \matrix{ x \ge 0 \hfill \cr \sqrt x = 7 \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{ x \ge 0 \hfill \cr {\left( {\sqrt x } \right)^2} = {\left( 7 \right)^2} \hfill \cr} \right.\) \( \Leftrightarrow \left\{ \matrix{ x \ge 0 \hfill \cr x = 49 \hfill \cr} \right. \Leftrightarrow x = 49\)
Câu c:
\(\sqrt x < \sqrt 2 \Leftrightarrow \left\{ \matrix{
x \ge 0 \hfill \cr
{\left( {\sqrt x } \right)^2} < {\left( {\sqrt 2 } \right)^2} \hfill \cr} \right. \) \(\Leftrightarrow 0 \le x < 2\)
Câu d:
\(\sqrt {2x} < 4 \Leftrightarrow \left\{ \matrix{
2x \ge 0 \hfill \cr
{\left( {\sqrt {2x} } \right)^2} < {\left( 4 \right)^2} \hfill \cr} \right. \) \(\Leftrightarrow \left\{ \matrix{
x \ge 0 \hfill \cr
2x < 16 \hfill \cr} \right. \)
\( \Leftrightarrow \left\{ \matrix{
x \ge 0 \hfill \cr
x < 16:2 \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{
x \ge 0 \hfill \cr
x < 8 \hfill \cr} \right.\) \(\Leftrightarrow 0 \le x < 8\)
