Find the radius of the circle whose center is at (3, 2) and which passes through the point (9, -6).
Answer: B
The radius of the circle is the distance between its center and any point on its circumference. We use the distance formula to find the distance between (3, 2) and (9, -6).
Radius (r) = \(\sqrt{(x_2-x_1)^2 + (y_2-y_1)^2}\)
r = \(\sqrt{(9-3)^2 + (-6-2)^2}\)
r = \(\sqrt{6^2 + (-8)^2}\)
r = \(\sqrt{36 + 64} = \sqrt{100} = 10\) units.