Level
pending

If

$\biggl(\sin\alpha \sec ^{ 2 }{ \frac { \alpha }{ 2 } } =l\biggr)$ and $\left( 1+\tan { \frac { \alpha }{ 2 } } -\sec { \frac { \alpha }{ 2 } } \right) \left( 1+\tan { \frac { \alpha }{ 2 } } +\sec { \frac { \alpha }{ 2 } } \right) =Cl$

Find $C$