Answer :
[tex]\bf \textit{area of a sector of a circle}\\\\ A=\cfrac{\theta \pi r^2}{360}~~ \begin{cases} \theta = angle~in\\ \qquad degrees\\ r=radius\\[-0.5em] \hrulefill\\ r=1\\ \theta =90 \end{cases}\implies A=\cfrac{90\pi (1)^2}{360}\implies A=\cfrac{\pi }{4}\implies A\approx 0.79[/tex]