Question 887540
Complete the Square for the y, and put the equation into standard form.


<a href="http://www.algebra.com/tutors/Completing-the-Square-to-Solve-General-Quadratic-Equation.lesson?content_action=show_dev">Click to see lesson that includes how to complete the square.</a>


Adjust the equation into {{{x^2+(y-k)^2=r^2}}}.
In your example, the x coordinate of the center is 0.  The center of your circle will be some point, (0,k)  and radius is r.