## Understanding Radian Measure

A circle O with radius 1 unit has its center placed at the origin. Let *A* be its intersection with the *x*-axis at (1,0) and* P* be another point on its circumference. If we move *P* along its circumference, then we can determine the distance traveled by *P*. If we let* A* be the starting point of* P* as it moves counterclockwise, then the distance traveled by *P* is equal to the length of arc *AP* represented by the red arc in the following figure.

To be able to know the length of arc *AP*, first, we must know the total distance traveled by *P *from *A* going counterclockwise and back to *A* (i.e. complete revolution). That is, we need to find the circumference of the circle. Since a unit circle has radius 1 unit, its circumference *C* is » Read more