Find the area of a circular sector from its radius and central angle.
The area of a sector is a fraction of the full circle's area, proportional to the central angle.
Sector Area
A = ½ × r² × θ (θ in radians)
Sector area = (θ/360°) × πr². It's the proportional slice of the full area.
For θ = 180° (π radians): A = ½ × r² × π = πr²/2.