Geometry · Circles
Diameter
HSG-C.A.2
Definition
A segment through the center of a circle with both endpoints on the circle, equal to twice the radius.
Examples
- d = 2r, so a circle with radius 4 has a diameter of 8.
- A diameter is the longest chord that can be drawn in a circle.
Key rule
A diameter always passes through the center.
Memory hook
Straight through the center — twice the radius.