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How to Find the Radius from the Diameter (Mathematics Lesson)

What Is the Diameter in Terms of the Radius?

The diameter of a circle is twice the radius.

How to Find the Diameter from the Radius

Question: What is the diameter of the circle, with radius r, below?



Step 1: Multiply the radius, r, by 2.
r × 2 = 2r

This is the diameter, d, of the circle.

A Real Example of How to Find the Diameter from the Radius

Question: What is the diameter of the circle, with radius 5cm, below?



Step 1: Multiply the radius, 5cm, by 2.
5 × 2 = 10cm

The diameter of the circle is 10cm.
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Note
WHAT IS A CIRCLE?

A circle is a shape containing a set of points that are all the same distance from the center. This distance is the radius.



The diameter is the line through the center of the circle that has its endpoints on the circle.