${{\sqrt 2 } \over {\sqrt {(2 + \sqrt 3 )} - \sqrt {(2 - \sqrt 3 } )}} = $
$0$
$1$
$\sqrt 2 $
$1/\sqrt 2 $
The rationalising factor of $2\sqrt 3 - \sqrt 7 $ is
If $a = \sqrt {(21)} - \sqrt {(20)} $ and $b = \sqrt {(18)} - \sqrt {(17),} $ then
If ${x^{x\root 3 \of x }} = {(x\,.\,\root 3 \of x )^x},$ then $x =$
${a^{m{{\log }_a}n}} = $
The rationalising factor of ${a^{1/3}} + {a^{ - 1/3}}$ is