Mathematics 1560 Lecture Notes - Lecture 3: Central Angle, Radian, Unit Circle
Document Summary
The number of radians in the central angle a cb within a circle of radius r is de ned as the number of radius units contained in the arc s subtended by the central angle. With the central angle measuring radians, this means = s/r or s = r . One complete revolution of the unit circle is 360 or 2 radians. Radians are a unitless measure of angles and we need not write radians (though we often will). Degrees are not unitless and if we measure angles in degrees then we must include the degrees symbol . classes, we will only rarely use degrees to measure angles and will almost. An angle in the xy-plane is in standard position if its vertex lies at the origin and its initial ray lies along the positive x-axis. Angles measured counterclockwise from the positive x-axis are assigned positive measures; angles measured clockwise are assigned negative measures.
