How do you find the equation of a circle?

Find the equation of a circle using the formula (x-h)squared+(y-k)squared=r squared. Know that h and k represent the coordinates for the center, with h being the x value, k being the y value and r being the radius.

1. Find the coordinates

   Determine what the coordinates are for the center and what the radius equals.

2. Insert the coordinates and the radius value into the equation

   Plug the coordinates and the radius value into the equation by substituting the information in place of the corresponding variable.

3. Watch the signs

   If the center is negative, the negative sign in the equation becomes positive. If the center is positive, the sign in the equation stays the same.