Circle area and circumference
Area = πr²; circumference = 2πr (or πd). Arc length and sector area for parts.
Memorise: A = πr², C = 2πr. For a sector with angle θ (in degrees): arc length = (θ/360) × 2πr; sector area = (θ/360) × πr².
Worked examples
Circle r=5: A = 25π ≈ 78.5; C = 10π ≈ 31.4.
Sector 60° of r=6: arc = (60/360)×12π = 2π ≈ 6.28; area = (60/360)×36π = 6π ≈ 18.85.
Diameter d = 14: C = 14π ≈ 44 cm.
Frequently asked questions
Leave in π?
GCSE often expects ‘in terms of π’ for exact answers. Decimal form when asked to a number of significant figures.
Radians?
Not for GCSE — A-Level only. GCSE sectors use degrees.