The rationalising factor of ${a^{1/3}} + {a^{ - 1/3}}$ is
${a^{1/3}} - {a^{ - 1/3}}$
${a^{2/3}} + {a^{ - 2/3}}$
${a^{2/3}} - {a^{ - 2/3}}$
${a^{2/3}} + {a^{ - 2/3}} - 1$
The value of ${{15} \over {\sqrt {10} + \sqrt {20} + \sqrt {40} - \sqrt 5 - \sqrt {80} }}$ is
${{{{2.3}^{n + 1}} + {{7.3}^{n - 1}}} \over {{3^{n + 2}} - 2{{(1/3)}^{l - n}}}} = $
If $x = 3 - \sqrt {5,} $ then ${{\sqrt x } \over {\sqrt 2 + \sqrt {(3x - 2)} }} = $
$\sqrt {(3 + \sqrt 5 )} - \sqrt {(2 + \sqrt 3 )} = $
The greatest number among $\root 3 \of 9 ,\root 4 \of {11} ,\root 6 \of {17} $ is