Finding the Cen.tre

---

Most people learn only the standard ways to find a circle’s centre or radius—using a square and straightedge, constructing perpendiculars from two chords, or using a centre-finding tool. These methods work, but they’re not the whole story.

Below are several lesser-known geometric techniques based on simple constructions. Using a compass and straightedge, they reveal a circle’s centre or radius in surprisingly simple and elegant ways, with formulas provided where useful.

Explore the interactive apps below to see these methods in action—and discover alternatives to traditional chord-and sagitta-based measurement