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Chords and Diameters

Part of the Circles section of Coddy's Geometry journey. Lesson 2 of 59.

A circle is all the points at the same distance from one point, its center. That distance is the radius. For the goat, it is the 5 m rope. Every radius of a circle has the same length.

$Circle O with a diameter AB of 10, a radius OC of 5 and a chord DE$

A segment is a straight line between two points.
A chord is a segment between two points on the circle, like DE.
A diameter is a chord that goes through the center, like AB. It is two radii end to end, so a diameter is twice the radius.
When a point cuts a segment into two pieces, the pieces add up to the whole segment.

Challenge

BD is a diameter of circle O. It is 12 long. The segment OP is 10 long and crosses the circle at A. Find AP.

Then press Check.

Try it yourself

$Find the marked part of the figure$

Find the marked part of the figure

All lessons in Circles

1Parts of a Circle

Center and RadiusChords and DiametersRecap: 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 Inside Around the Circle Radius 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