\(\sqrt{\dfrac{7-3\sqrt{5}}{162}}\)
\(=\dfrac{\sqrt{7-3\sqrt{5}}}{\sqrt{162}}\)
\(=\dfrac{\sqrt{2}\cdot\sqrt{7-3\sqrt{5}}}{9\sqrt{2}\cdot\sqrt{2}}\)
\(=\dfrac{\sqrt{14-6\sqrt{5}}}{9\cdot2}\)
\(=\dfrac{\sqrt{3^2-2\cdot3\cdot\sqrt{5}+\left(\sqrt{5}\right)^2}}{18}\)
\(=\dfrac{\sqrt{\left(3-\sqrt{5}\right)^2}}{18}\)
\(=\dfrac{3-\sqrt{5}}{18}\)