What is a radius of a circle? What about the diameter? Warm-Up What is a radius of a circle? What about the diameter? What is the origin of a graph? What is the center of a circle?

Circle Equations

Use equations to graph circles What we will Learn Use equations to graph circles Given points and the radius/diameter give the equation of a circle

Circle at the origin

What is the equation for a circle with a center at (0, 0) and Example 1 What is the equation for a circle with a center at (0, 0) and radius = 5?

Circle not on the origin (x – h)2 + (y – k)2 = r2 when the center is at point (h, k)

What is the center and radius of the circle with equation Example 2 What is the center and radius of the circle with equation (x+5)+(y-4)=64

What are the coordinates of the center of a circle, whose diameter Example 3 What are the coordinates of the center of a circle, whose diameter has endpoints at (–3, 9) and (10, 18)?

Example 4

Example 5

Example