Page 98 - IM_FL_Geometry_Print Sample

This ratio of arc length to radius is constant no matter what arc is drawn on the angle. This ratio is called the radian measure of the angle. The radian measure of a 60 degree angle happens to be roughly 1.05. In other words, a 60 degree angle will always trace out an arc length that is about 1.05 times the radius.
So we now have a new way to measure an angle. Create a circle of any size centered at the vertex of the angle. The angle traces out an arc of the circle. The radian measure of the angle is the ratio of arc length to radius. In other words, the radian measure of the angle is de ned by , where is the arc length traced out by the angle and is the radius of the arc.
Unit 7
Lesson 2: Measuring Angles
25