The standard circle equation is (x – h)2 + (y – k)2 = r2, with the coordinate of the center being (h,k) and the radius being r.
A problem might be,
A circle has a radius of √5 units and is centered at (2.1,-5.4). What’s the equation of the circle?
We can solve this using the circle equation.
(x – h)2 + (y – k)2 = r2, and h is the x-coordinate of the center which is 2.1, k is the y-coordinate of the center which is -5.4, and r is the radius of the circle which is √5. We can rewrite the equation as (x – 2.1)2 + (y – (-5.4))2 = √52, or (x – 2.1)2 + (y + 5.4)2 = 5.