[tex]\textit{area of a sector of a circle}\\\\ A=\cfrac{\theta \pi r^2}{360}~~ \begin{cases} r=radius\\ \theta =\stackrel{degrees}{angle}\\[-0.5em] \hrulefill\\ r=20\\ \theta =90 \end{cases}\implies \begin{array}{llll} A=\cfrac{(90)\pi (20)^2}{360}\implies A=100\pi \\\\\\ A\approx 314.2 \end{array}[/tex]
