Learning Resources

Investigation 1: Distances on a Circle

• A radian is a unit of angle measurement.
• An angle of one radian lies between two radii of a circle that cut, between them, an arc on the circumference equal in length to the radius.
• Since the circumference of a circle is 2 times its radius, there are 2 radians in a circle.
• The symbol for radian measure is rad. However, often the word rad is omitted. For example, cos 5rad is often written cos 5 for convenience. The absence of the degree symbol indicates it is 5 radians rather than 5 degrees.