Answer: D
Let \(a = \frac{1}{5 + 2\sqrt{6}}\) Then, \(\frac{1}{a} = 5 + 2\sqrt{6}\) Now, \(a = \frac{1}{5 + 2\sqrt{6}} = \frac{5 - 2\sqrt{6}}{(5 + 2\sqrt{6})(5 - 2\sqrt{6})} = \frac{5 - 2\sqrt{6}}{25 - 24} = 5 - 2\sqrt{6}\) So, \(a + \frac{1}{a} = 5 - 2\sqrt{6} + 5 + 2\sqrt{6} = 10\) \(a - \frac{1}{a} = 5 - 2\sqrt{6} - 5 - 2\sqrt{6} = -4\sqrt{6}\) Therefore, \(a^2 - \frac{1}{a^2} = (a + \frac{1}{a})(a - \frac{1}{a}) = 10 \times (-4\sqrt{6}) = -40\sqrt{6}\)
Let \(a = \frac{1}{5 + 2\sqrt{6}}\) Then, \(\frac{1}{a} = 5 + 2\sqrt{6}\) Now, \(a = \frac{1}{5 + 2\sqrt{6}} = \frac{5 - 2\sqrt{6}}{(5 + 2\sqrt{6})(5 - 2\sqrt{6})} = \frac{5 - 2\sqrt{6}}{25 - 24} = 5 - 2\sqrt{6}\) So, \(a + \frac{1}{a} = 5 - 2\sqrt{6} + 5 + 2\sqrt{6} = 10\) \(a - \frac{1}{a} = 5 - 2\sqrt{6} - 5 - 2\sqrt{6} = -4\sqrt{6}\) Therefore, \(a^2 - \frac{1}{a^2} = (a + \frac{1}{a})(a - \frac{1}{a}) = 10 \times (-4\sqrt{6}) = -40\sqrt{6}\)