Đáp án:
$\begin{array}{l}
a)Đkxđ:\frac{2}{3}x + 5 \ge 0 \Rightarrow x \ge - \frac{{15}}{2}\\
\sqrt {\frac{2}{3}x + 5} = 3\\
\Rightarrow \frac{2}{3}x + 5 = 9\\
\Rightarrow \frac{2}{3}x = 4\\
\Rightarrow x = 6\left( {tmdk} \right)\\
b)Đkxđ:\left\{ \begin{array}{l}
{x^2} - 7x + 10 \ge 0\\
x - 1 \ge 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
\left( {x - 2} \right)\left( {x - 5} \right) \ge 0\\
x \ge 1
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \ge 5\\
1 \le x \le 2
\end{array} \right.\\
\sqrt {{x^2} - 7x + 10} = x - 1\\
\Rightarrow {x^2} - 7x + 10 = {x^2} - 2x + 1\\
\Rightarrow 5x = 9\\
\Rightarrow x = \frac{9}{5}\left( {tmdk} \right)\\
c)\left\{ \begin{array}{l}
- 7x + 3y = - 5\\
5x - 2y = 4
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
- 35x + 15y = - 25\\
35x - 14y = 28
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
y = 3\\
5x - 2y = 4
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
y = 3\\
5x = 2.3 + 4
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
y = 3\\
x = 2
\end{array} \right.
\end{array}$
