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  • The locus of points distance $\displaystyle {r}$(radius) from center ${O}$
  • A cross section of a cone or cylinder parallel to the base. For more on this, see Dandelin Spheres, a commonly used method of deriving all conic sections.
  • $(x - a)^{2} + (y - b)^{2} = r^{2}$ for a circle centered at $(a,b)$ with radius ${r}$


  • Area $\displaystyle \pi r^2$
  • circumference $\displaystyle 2\pi r$

Other Properties

  • The perpendicular bisector of any chord in the circle is a diameter
  • awaiting diagrams to add stuff on inscribed angles + tangents.

Practice Problems

See Also

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