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radius

Primary Information
Secondary Information

Definition

A radius is a line segment that goes from the centre of a circle to the edge of the circle. It is the distance from the centre of the circle to any point on the circle.

For example, if you draw a circle on a piece of paper, you can measure the radius by drawing a line from the centre of the circle to any point on the circle. The distance between the two points is the radius.

How can the word be used?

The radius of the circle is 10 cm.

radius

Different forms of the word

Noun:

  • a straight line from the centre of a circle or sphere to the circumference.
  • a line segment joining the centre of a circle or sphere with any point on the circumference.
  • a bone of the forearm, extending from the elbow to the wrist.

Etymology

The word "radius" comes from the Latin word "radius", which means "ray".

The first recorded use of the word "radius" in English was in the 14th century.

Question

Why might it be useful to know the radius of a circle?