The conjugate surd of $\left(\sqrt{3}-5\right)$ is 

The conjugate surd of the surd $-\left(2+\sqrt{3}\right)$ is $-a+\sqrt{3}$. Then $a=$_____.

Two similar surds among the surds $\sqrt{32}, \sqrt{75}, \sqrt{80}$ and $\sqrt{108}$ are $\sqrt{75}$ and $\sqrt{a}$. Then $a=$_____.

The least rationalizing factor of $\sqrt{18}$ is $\sqrt{a}$. Then $a=$_____.

If $x+\sqrt{x^2-9}=9$, then $x-\sqrt{x^2-9}=$_____.