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