(a) Evaluate: (5 cos^2 60^°+4 sec^2 30^°- tan^2 45^°)/(sin^2 30^°+ sin^2 60^°)

Evaluate : $\displaystyle \frac{5 \cos ^{2} 60^{\circ}+4 \sec ^{2} 30^{\circ}-\tan ^{2} 45^{\circ}}{\sin ^{2} 30^{\circ}+\sin ^{2} 60^{\circ}}$

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