Big Ideas:
A circle’s central angle is equivalent to its corresponding arc length. When a circle has a central angle = 1, arc length = 1, and this special circle is called the unit circle.
This lesson builds on what students learn in geometry about angles and arc length. In this lesson, students will learn the meaning of a radian. Through investigation of a circle, students will discover the relationship between the radius and the circumference. Students will start to derive the equation for converting between radians and degrees. This builds toward the take away that it takes 6.28 radians to move around the circumference of a circle and that a radian represents the circumference of a circle divided by the radius.
Vocabulary: radian
Lesson plan