\(P=\sqrt{14+6\sqrt{5}}+\sqrt{14-6\sqrt{5}}\)
\(=\sqrt{3^2+6\sqrt{5}+\sqrt{5}^2}+\sqrt{3^2-6\sqrt{5}+\sqrt{5}^2}\)
\(=\sqrt{\left(3+\sqrt{5}\right)^2}+\sqrt{\left(3-\sqrt{5}\right)^2}\)
\(=\left|3+\sqrt{5}\right|+\left|3-\sqrt{5}\right|\)
\(=3+\sqrt{5}+3-\sqrt{5}\)
\(=6\)