Course: College Algebra
Topic: Basic Geometry
Subtopic: Circles


A circle is the two-dimensional shape formed by connecting all the points that lie at a fixed distance from a given central point. A circle is a basic geometrical object with many practical uses and mathematical history.

Equation of a circle with center (h,k) and radius r: `(x-h)^2+(y-k)^2=r^2`


By the end of this topic you should know and be prepared to be tested on:


Terms you should be able to define: circle, center, radius, diameter, circumference `C=piD`, area `A=pir^2`, standard form `(x-h)^2+(y-k)^2=r^2`, general form `y=ax^2+bx+cy^2+dy+e`, chord of a circle, tangent line to a circle

Mini-Lectures and Examples

STUDY: Geometry - Distance Formula, Midpoint Formula, and Circles

Supplementary Resources (recommended)

A fun read: Quite Interesting Facts About Circles from The Telegraph in the U.K.

Supplemental Resources (optional)

If you need supplemental tutorial videos with examples relevant to this section go to James Sousa's MathIsPower4U and search for topics: "Graphing and Writing Equations of Circles"

rev. 2020-10-10