[tex]\textit{area of a sector of a circle}\\\\ A=\cfrac{\theta r^2}{2} ~~ \begin{cases} r=radius\\ \theta =\stackrel{radians}{angle}\\[-0.5em] \hrulefill\\ r=4\\ \theta =\frac{\pi }{4} \end{cases}\implies A=\cfrac{ ~~ \frac{\pi }{4} ~~ (4)^2}{2}\implies A=2\pi \implies A\approx 6.28[/tex]
