Writing the Equation of a Circle
In order to write the equation for a circle you need to start with the standard equation:
(x – h)2 + (y – k)2 = r2
Suppose you know that a circle has a center at (-1, 4) and has a radius of 5 units. What is the equation of this circle?
From the given information we know h = -1, k = 4, and r = 5. We can then insert this information into our general equation.
(x – (-1))2 + (y – 4)2 = 52
(x + 1)2 + (y – 4)2 = 25
This is the final equation of this particular circle.
