# Equation of a circle

4 videos
2 skills
You know that a circle can be viewed as the set of all points that whose distance from the center is equal to the radius. In this tutorial, we use this information and the Pythagorean Theorem to derive the equation of a circle.

### Equation for a circle using the Pythagorean Theorem

VIDEO 6:19 minutes

### Pythagorean theorem and radii of circles

VIDEO 5:53 minutes

### How to find the center and radius of a circle from its standard equation (example)

VIDEO 3:51 minutes
Sal finds the center and the radius of the circle whose equation is (x+3)^2+(y-4)^2=49.

### Find the features of a circle from its standard equation

PRACTICE PROBLEMS
Find the center and radius of a circle given the equation in standard form.

### How to find the center and radius of a circle from its expanded equation (example)

VIDEO 4:20 minutes
Sal finds the center and the radius of a circle whose equation is x^2+y^2+4x-4y-17=0, and then he graphs the circle.

### Find the features of a circle from its expanded equation

PRACTICE PROBLEMS
Find the center and radius of a circle given the equation in expanded form.