This is a 45 page Smartboard file on how to write the equation of a circle. Students are introduced to the equation of a circle. They first learn how to write the equation when given a center point and a radius. Students then look at the equations and pick out the x and y coordinates and figure the radius. Students also have to write the equation if given a diameter which causes them to use the distance formula and midpoint formula. There are several pages of practice with answers.