Students write the equation for a circle in center-radius form, (x - a)^2 + (y - b)^2 = r^2 using the Pythagorean theorem or the distance formula. Students write the equation of a circle given the center and radius. Students identify the center and radius of a circle given the equation.

Teacher and Student versions of full lesson from engageNY

Students complete the square in order to write the equation of a circle in center-radius form. Students recognize when a quadratic in x and y is the equation for a circle.

Teacher and Student versions of full lesson from engageNY

Learning Objectives: Graph a circle. Find the equation of a circle in the coordinate plane. Find the radius and center, given the equation of a circle and vice versa. Find the equation of a circle, given the center and a point on the circle.

Lesson, videos, exercises, and text from CK-12. Additional resources available at this site.