Geometrical Properties of Circles

1. tan ⊥rad

2. ∠ at centre = 2 ∠ at circumference

3. ∠s in same segment

4. ∠ in semicircle

5. ∠s in opp. segments  OR  opp. ∠s in cyclic quad.

6. ∠s in alt. segments  OR  alt. segment theorem

7. tangents from an external point