Lesson 11.3: Areas of Circles and Sectors
Key Concepts: Areas of Circles and Sectors
Area of a Circle
A = πr²
Area of a Sector
A sector is a "pie slice" of a circle defined by a central angle θ.
A = (θ/360°) × πr²
Area of a Segment
A segment is the region between a chord and its arc.
A(segment) = A(sector) − A(triangle)
Key Ideas
- The ratio of a sector's area to the circle's area equals the ratio of the central angle to 360°.