1. Notes 6-1: Radian Measure
Radian: The length of the corresponding arc on a unit circle.
Arc: A “piece” of the circumference.
Sector: A portion or “slice” of a circle.
The arc length of the sector is the radian measure of θ.

2. C = 2πr (or C=πd) since r = 1 C = 2π(1) C = 2π Circumference:
unit circle: radius = 1
1 full circle = 360° = 2π radians
so…180° = π radians

3. Summary:

4. Finding the length of an arc on any circle.
s = arc length
r = radius
θ = central angle in radians
If the angle is given in degrees, then convert to radians before calculating the arc length.

6. p Change 240° to radians.

7. 9. Evaluate each expression without a calculator
9. Evaluate each expression without a calculator. (In other words, draw a unit circle and find the exact value.)
*See next page for final solutions…

8. 9. Now answer the given expressions (including part b and c)

9. Given the measurement of a central angle, find the length of its intercepted arc in a circle of radius 15 inches. Round to the nearest tenth. Reminder: s = rθ