Đặt \(A=\sqrt{9+\sqrt{13}}+\sqrt{9-\sqrt{13}}\)
\(\Rightarrow A^2=9+\sqrt{13}+9-\sqrt{13}+2\sqrt{\left(9+\sqrt{13}\right)\left(9-\sqrt{13}\right)}\)
\(\Rightarrow A^2=18-2\sqrt{9^2-13}\)
\(\Rightarrow A^2=18-4\sqrt{17}\)
\(\Rightarrow A=\sqrt{18-4\sqrt{17}}\)