Question #N324
A circle in the $xy$-plane has a diameter with endpoints $(-4,5)$ and $(6,5)$. What is the length of the radius of this circle?
A. 1
B. 5
C. 10
D. 20
Correct Answer is: B
The radius of a circle is half the length of the diameter. The length of the diameter can be found using the distance formula: $\sqrt{(6 - (-4))^2 + (5 - 5)^2} = \sqrt{10^2 + 0^2} = 10$. The radius is half this length, which is 5.