| Equation of circle in various forms |
| Parametric Equation of a Circle |
| Position of a Point with respect to Circle |
| Equation of Tangent , Equation of Normal on the Circle |
| Chord of Contact of Tangents |
| Equation of Radical Axis of two circles |
| Equation of Family of Circles , Angle of Intersection of two Circles |
| External and Internal Contacts of Circles , Common Tangents to Two Circles |