Ta có \(z(2+i) + \overline{z} = 5+3i \Leftrightarrow (a+bi)(2+i) + a - bi = 5 + 3i\) \(3a - b + (a+b)i = 5 + 3i\) \(\Leftrightarrow \left\{\begin{matrix} 3a - b = 5\\ a + b = 3 \end{matrix}\right. \Leftrightarrow \left\{\begin{matrix} a = 2\\ b = 1 \end{matrix}\right.\) Do đó \(|z| = \sqrt{2^2 + 1^2} = \sqrt{5}\)