## MEASURE OF AN ANGLE

**READ** the instructions on the *right* and **INTERACT** with the GeoGebra applet below.

Steven Lapinski, October 2007 Created with GeoGebra

## Investigation Steps

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- 1. What are the measures of the blue radius and the red arc?

- 2. Move point A and observe: What measurements change? What measurements stay the same?

- 3. Move point P until the measure of the arc equals the radius. This measure correspondes to 1 radian.

- 4. What angle is bigger, the one that measures 1 radian or one that measures 60°?

- 5. Move Point P so that the angle measures 2 radians, how many degrees would that be? Would an angle of 3 radians be greater or less than 180°?

- 6. In your own words, write a definition of a radian.

- 7. Imagine a 180° angle, what is the measure in radians? Is this reasonable? How many radians is a 90° angle? A 360°? why?