Which term is the length of a line segment between the center and the circumference of a circle or sphere?

• A. Diameter
• B. Area
• C. Radius
• D. Perimeter

Answer: (C)

The radius is the distance from the center to the edge of a circle or sphere. This length is the same in every direction, so all radii are equal for a given circle or sphere. The diameter is twice the radius and goes across the circle or sphere through the center, from one edge to the opposite edge. Area measures how much space the interior contains, not a distance from the center. Perimeter is the distance around a 2D shape (for a circle, this is called the circumference). Since the question asks for the length from the center to the edge, the term is radius.