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

What Is the Radius in Terms of the Circumference?

The radius of a circle is the circumference of a circle divided by 2π.

How to Find the Radius from the Circumference

Question: What is the radius of the circle, with circumference C, below?



Step 1: Divide the circumference, C, by 2.
C ÷ 2 = C2

Step 2: Divide by π.
C2 ÷ π = C

This is the radius, r, of the circle.

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

Question: What is the radius of the circle, with circumference 50cm, below?



Step 1: Divide the circumference, 50cm, by 2.
50 ÷ 2 = 25cm

Step 2: Divide by π.
25 ÷ π = 8cm

The radius of the circle is 8cm.

Another Real Example of How to Find the Radius from the Circumference

The slider below shows another real example of how to find the radius of a circle from the circumference:
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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.