Evaluate :

$\dfrac{4 - \sqrt{5}}{4 + \sqrt{5}} + \dfrac{4 + \sqrt{5}}{4 - \sqrt{5}}$

If $\dfrac{2 + \sqrt{5}}{2 - \sqrt{5}} = x \text{ and } \dfrac{2 - \sqrt{5}}{2 + \sqrt{5}} = y$; find the value of x² - y².

$\sqrt{27}$ is irrational and $\sqrt{3}$ is also irrational, then which of the following is rational:

1. $\sqrt{27} - \sqrt{3}$

2. $\sqrt{27} + \sqrt{3}$

3. $\sqrt{27} \times \sqrt{3}$

4. none of these

If x = $\sqrt{6} - \sqrt{5}$, then $x - \dfrac{1}{x}$ is equal to:

1. 1

2. 11

3. $2\sqrt{6}$

4. -2 $\sqrt{5}$