Answer
$\dfrac {9}{2}=4.5$
Work Step by Step
$A=\int ^{\pi /2}_{0}\dfrac {1}{2}r^{2}d\theta =\int ^{\pi /2}_{0}\dfrac {1}{2}\times \left[ 9\sin 2\theta \right] d\theta =-\dfrac {9}{4}\cos 2\theta ]^{\dfrac {\pi }{2}}_{0}=\dfrac {9}{4}-\left( -\dfrac {9}{4}\right) =\dfrac {9}{2}=4.5$
