Question #N238
In the xy-plane, a circle has a diameter with endpoints at (1, 4) and (5, 2). What is the length of the radius of the circle?
A. 2
B. 4
C. 5
D. 10
Correct Answer is: A
The radius of a circle is half the length of the diameter. The length of the diameter can be found using the distance formula: \sqrt{(5-1)^2 + (2-4)^2} = \sqrt{4^2 + (-2)^2} = \sqrt{20} = 2\sqrt{5}. The radius is half of this length, or \sqrt{5}, which is equal to 2.