Official solution
x = \[\sqrt {{2^{\cos e{c^{ - 1}}t}}} \]
\[\therefore\,\,\,\,\] \[{{dx} \over {dt}}\] = \[{1 \over {2\sqrt {{2^{\cos e{c^{ - 1}}t}}} }}\] \[ \times \] (\[{2^{\cos e{c^{ - 1}}t}}\,.\,\log 2\]) \[ \times \] \[{{ - 1} \over {t\sqrt {{t^2} - 1} }}\]
\[{{dy} \over {dt}}\] = \[{1 \over {2\sqrt {{2^{{{\sec }^{ - 1}}t}}} }}\] \[ \times \] \[\left( {{2^{{{\sec }^{ - 1}}t}}\log 2} \right)\] \[ \times \] \[{1 \over {t\sqrt {{t^2} - 1} }}\]
\[\therefore\,\,\,\,\] \[{{dy} \over {dx}}\]
= \[{{{{dy} \over {dt}}} \over {{{dx} \over {dt}}}}\]
= \[{{ - \sqrt {{2^{\cos e{c^{ - 1}}t}}} } \over {\sqrt {{2^{\cos e{c^{ - 1}}t}}} }}\] \[ \times \] \[{{{2^{{{\sec }^{ - 1}}t}}} \over {{2^{\cos e{c^{ - 1}}t}}}}\]
= \[ - \sqrt {{{{2^{{{\sec }^{ - 1}}t}}} \over {{2^{\cos e{c^{ - 1}}t}}}}} \]
= - \[{y \over x}\]