In Figure 1.4.3, sector POA is part of a circle of radius 1, the length of the segment OA. This sector is a fractional part of that circle, which has an area of $\mathrm{\π} {\left(1\right)}^2\=\mathrm{\π}$. The fractional part of the area is the ratio of the angle $\mathrm{\θ}$ to $2 \mathrm{\π}$, the full circle. Hence, the area of sector POA is $\frac{\|\mathrm{\θ}\|}{2 \mathrm{\π}}\left(\mathrm{\π}\right)\=\frac{\left|\mathrm{\θ}\right|}{2}$.