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A circle has radius 1 unit. Find the length of the arc defined by each of these central angles. Give your answers in terms of .
There is a circular path around a pond with a fountain in the center. The path is 2 miles long. When Tyler enters the path, he is east of the fountain. He starts walking counterclockwise.
Suppose we have a circle that has a central angle. The radian measure of the angle is the ratio of the length of the arc defined by the angle to the circle’s radius. That is, .
Degrees are one way to measure the size of an angle. Radians are another way to measure angles. Assume an angle’s vertex is the center of a circle. The radian measure of the angle is the ratio between the length of the arc defined by the angle and the radius of the circle. We can write this as . This ratio is constant for a given angle, no matter the size of the circle.
Consider a 180-degree central angle in a circle with radius 3 units. The arc length defined by the angle is units. The radian measure of the angle is the ratio of the arc length to the radius, which is radians because .
Another way to think of the radian measure of the angle is that it measures the number of radii that would make up the length of the arc defined by the angle. For example, if we draw an arc that is the same length as the radius, both the arc length and the radius are 1 unit. The radian measure of the central angle that defines this arc is the quotient of those values, or 1 radian.
A radian is a unit of measurement for angles, based on the radius of a circle.
The radian measure of any central angle is this ratio: