CON002 · Conic sections · Classes 11–12
Conic Section: Circle
Cutting a cone with a plane perpendicular to its axis gives a circle.
Conic Section: Circle📐 Formula
For cone half-angle α and plane angle β to the axis, eccentricity e = cos β ÷ cos α. β = 90° → e = 0 (circle).
✏️ Worked example
α = 30°, β = 90°: e = 0 → circle.
🌍 Where it is used
Circular cross-sections of funnels and lamp shades.
❓ Quick check
The eccentricity of a circle is…