CALCULUS Understanding Its Concepts and Methods

Cosine function

The trigonometric functions are circular functions, because they are defined in terms of a circle.

Draw a circle of radius 1 with center at the origin.

Draw a line from the origin at an angle *q* to the positive *x*-axis.

The line intersects the circle at a point
(*x*,*y*) as shown
in the following figure:

The cosine of the angle *q* is defined to be cos *q*
= *x*. In the figure,
the green (if positive) or red (if negative) arc length on the
circle is equal to the green or red horizontal line segmentt.

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Copyright © 2006 Darel Hardy, Fred Richman, Carol Walker, Robert Wisner. All rights reserved. Except upon the express prior permission in writing, from the authors, no part of this work may be reproduced, transcribed, stored electronically, or transmitted in any form by any method.