${{{{[4 + \sqrt {(15)} ]}^{3/2}} + {{[4 - \sqrt {(15)} ]}^{3/2}}} \over {{{[6 + \sqrt {(35)} ]}^{3/2}} - {{[6 - \sqrt {(35)} ]}^{3/2}}}} = $
$1$
$7/13$
$13/7$
None of these
If ${\left( {{2 \over 3}} \right)^{x + 2}} = {\left( {{3 \over 2}} \right)^{2 - 2x}},$then $x =$
If ${x^y} = {y^x},$then ${(x/y)^{(x/y)}} = {x^{(x/y) - k}},$ where $k = $
${4 \over {1 + \sqrt 2 - \sqrt 3 }} = $
If ${a^x} = bc,{b^y} = ca,\,{c^z} = ab,$ then $xyz$=
If $x + \sqrt {({x^2} + 1)} = a,$ then $x =$