1. Lesson 10-3
Arcs
and Chords

2. Theorem #1:
In a circle, if two chords are congruent then their corresponding minor arcs are congruent. E A B C D
Example:

3. Theorem #2:
In a circle, if a diameter (or radius) is perpendicular to a chord, then it bisects the chord and its arc. E D A C B
Example:
If AB = 5 cm, find AE.

4. Theorem #3:
In a circle, two chords are congruent if and only if they are equidistant from the center. O A B C D F E
Example:
If AB = 5 cm, find CD.
Since AB = CD, CD = 5 cm.

5. Try Some Sketches:
Draw a circle with a chord that is 15 inches long and 8 inches from the center of the circle.
Draw a radius so that it forms a right triangle.
How could you find the length of the radius?
Solution:
∆ODB is a right triangle and
8cm
15cm O A B D x

6. Try Some Sketches: Draw a circle with a diameter that is 20 cm long.
Draw another chord (parallel to the diameter) that is 14cm long.
Find the distance from the smaller chord to the center of the circle.
Solution:
10 cm
20cm O A B D C
∆EOB is a right triangle.
OB (radius) = 10 cm
14 cm E x
7.1 cm