Question #N405
A circle with center (2, -1) is tangent to the x-axis. What is the radius of this circle?
A. 1
B. 2
C. 4
D. 8
Correct Answer is: A
Since the circle is tangent to the x-axis, the distance from the center of the circle to the x-axis is equal to the radius. The y-coordinate of the center is -1, so the radius of the circle is 1.