If $x + \sqrt {({x^2} + 1)} = a,$ then $x =$
${1 \over 2}(a + 1/a)$
${1 \over 2}(a - 1/a)$
$(a + {a^{ - 1}})$
None of these
${4 \over {1 + \sqrt 2 - \sqrt 3 }} = $
${{3\sqrt 2 } \over {\sqrt 6 + \sqrt 3 }} - {{4\sqrt 3 } \over {\sqrt 6 + \sqrt 2 }} + {{\sqrt 6 } \over {\sqrt 3 + \sqrt 2 }} = $
The value of the fifth root of $10^{10^{10}}$ is
If ${a^x} = {b^y} = {(ab)^{xy}},$ then $x + y = $
If ${a^x} = {(x + y + z)^y},{a^y} = {(x + y + z)^z}$, ${a^z} = {(x + y + z)^x},$ then