(d) $H = \frac{u^{2}\sin^{2}{45{^\circ}}}{2g} = \frac{u^{2}}{4g}$ …(i)
$R = \frac{u^{2}\sin{90{^\circ}}}{g} = \frac{u^{2}}{g}$
[image:4_image163.emf]
$\therefore\frac{R}{2} = \frac{u^{2}}{2g}$ …(ii)
$\therefore\tan\alpha = \frac{H}{R/2}$
$= \frac{\frac{u^{2}}{4g}}{\frac{u^{2}}{2g}} = \frac{1}{2}\ \therefore\ \alpha = \tan^{- 1}\left( \frac{1}{2} \right)$