Question

3. A circle with center (0,0) has a y-intercept at (3,0).
Find the equation of the circle.

Answer 1

x^2 + y^2 = 9

Explanation:

The standard equation of a circle with center at (h, k) and radius r is

(x - h)^2 + (y - k)^2 = r^2. Here h = 0, k = 0, x = 3 and y = 0:

(3 - 0)^2 + (0 - 0)^2 = r^2, or

9 = r^2. Thus, the radius is 3.

The equation of this circle is (x - 0)^2 + (y - 0)^2 = 9, or

x^2 + y^2 = 9