[tex]\bf \textit{area of a sector of a circle}\\\\
A=\cfrac{\theta r^2}{2}~~
\begin{cases}
r=radius\\
\theta =angle~in\\
\qquad radians\\
------\\
r=3\\
\theta =\frac{\pi }{4}
\end{cases}\implies A=\cfrac{\frac{\pi }{4}\cdot 3^2}{2}\implies A=\cfrac{\frac{9\pi }{4}}{2}
\\\\\\
A=\cfrac{9\pi }{4}\cdot \cfrac{1}{2}\implies A=\cfrac{9\pi }{8}[/tex]
