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Around the Circle

Part of the Circles section of Coddy's Geometry journey. Lesson 5 of 59.

Each side of the hexagon was as long as the radius. So the way around the hexagon is 6 radii, which is exactly 3 diameters. The circle curves outside the hexagon. So the way around the circle is a little more than 3 diameters.

The way around a circle is its circumference, C. For every circle, C divided by the diameter is the same number. This number is called π (pi), and it is about 3.14159. So

$C = \pi\cdot d$

$C = 2\cdot \pi\cdot r$

With a radius of 3, $C = 2\cdot \pi\cdot 3$ , which is 6π. Keep π as π: 6π is exact, while 18.85 is rounded.

Challenge

Circle O has radius 4. Find its circumference C. Leave π in the answer.

Then press Check.

Try it yourself

$Use the figure to find C$

Use the figure to find C

All lessons in Circles

1Parts of a Circle

Center and Radius Chords and Diameters Recap: Parts of a Circle

4Arcs and Sectors

Arc Length Area of a Sector Find the Central Angle The Missing Central Angle Recap: Arcs and Sectors

7Angles in a Semicircle

Thales' Theorem The Right Angle Inside Is That Enough?Semicircle With Letters Recap: Semicircles

10Tangents

What a Tangent Is Tangent and Radius Tangent Lengths Two Tangents From a Point Tangents With Letters Recap: Tangents

2Circumference

The Hexagon InsideAround the CircleRadius From Circumference Recap: Circumference

5Radii Make Isosceles

Two Radii, One Triangle Base Angles From the Center The Angle at the Center Isosceles With Letters Recap: Radii and Triangles

8Angles on the Same Arc

Same Arc, Same Angle Using the Same Arc Spot the Bow Tie Same Arc With Letters Recap: Same Arc

11Circle Chases

Tangent Meets Chord Two Roads to One Angle Enough to Find It?Cyclic Meets Isosceles Recap: Circle Chases