This cheat sheet covers the high school math concept – Circle.


This concept is a part of Coordinate Geometry (or Analytical Geometry), and is one of the important chapters in this area. It covers a wide range of topics including tangents, normals, chords and locus.

A strong grip on the basics of coordinate or analytical geometry is a must to solve problems related to Circle. A cheat sheet on Coordinate Geometry Basics is also available on this website.

This one page PDF covers summarized theory and the most important formulas related to the concept. Keep it handy while you’re revising the concept, especially before an exam.

The topics included in this cheat sheet are:

  • Standard Equation
  • Equation with known center and radius
  • Equation with known end-points of diameter
  • General Equation
  • Position of a point w.r.t. a Circle
  • Equation of Tangents: Slope Form and Point Form
  • Length of the Tangent from an External Point
  • Equation of Normal: Slope Form and Point Form
  • Chord of Contact
  • Chord with known Mid-Point
  • Family of Circles
  • Angle of Intersection of Circles
  • Orthogonal Intersection
  • Radical Axis
  • Relative Position of Two Circles
  • Common Tangents to Two Circles

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