$\frac{2 \tan 30^{\circ}}{1-\tan ^{2} 30^{\circ}} = ?$

In $\triangle PQR$, right-angled at $Q$, $PR + QR = 25 \, cm$ and $PQ = 5 \, cm$. Determine the values of $\sin P, \cos P$ and $\tan P$.

Evaluate:
$\cos 48^{\circ}-\sin 42^{\circ}$

If $\cot \theta = \frac{7}{8},$ evaluate:
$(i) \frac{(1+\sin \theta)(1-\sin \theta)}{(1+\cos \theta)(1-\cos \theta)}$
$(ii) \cot^2 \theta$

Prove the following identity,where the angles involved are acute angles for which the expressions are defined:
$\frac{\cos A}{1+\sin A}+\frac{1+\sin A}{\cos A}=2 \sec A$

If $\sin ( A - B ) = \frac{1}{2}$,$\cos ( A + B ) = \frac{1}{2}$,$0^{\circ} < A + B \leq 90^{\circ}$,and $A > B$,find $A$ and $B$.