Circles
Equations
When given the center and radius of a circle, substitute the values into the standard form. When the center or radius is not given, they will need to be found in order to write the equation of a circle.
Example 1 Find the equation for a circle with center at (15,-4) and with a radius of 8 units.
Substitute the center and radius into the standard form of a circle and simplify.
(x - (15))2 + (y - (-4))2 = 82
(x?15)2 + (y+4)2 = 64