Sine, Cosine, Tangent
Date: 03/13/2001 at 00:49:35 From: kelsie gale Subject: Sine, cosine, and tangent What are sine, cosine, and tangent?
Date: 03/13/2001 at 11:25:42 From: Doctor Rob Subject: Re: Sine, cosine, and tangent Thanks for writing to Ask Dr. Math, Kelsie! Sine, cosine, and tangent are functions that take an angle and give you a corresponding real number. Let A be an acute angle, and consider the following diagram: B"_,-' B'_,o' B _,o' | _,o' | | _,-' | | | _,-' | | | _,-' | | | _,-' | | | A o-------------------o---o---o----- C C' C" Here <ACB, <AC'B', and <AC"B" are all right angles. The three triangles ABC, AB'C', and AB"C", are similar. (Why?) That means their corresponding sides are in proportion to each other. This tells you that, for example, CB/AB = C'B'/AB' = C"B"/AB" That means that in a right triangle, no matter its size, the ratio of the leg opposite the angle A, to the hypotenuse, is a certain constant. That ratio is called the sine of the angle A, and is written sin(A). Similarly, the ratio of the leg adjacent to the angle, to the hypotenuse, AC/AB = AC'/AB' = AC"/AB" is a constant, called the cosine of the angle A, and written cos(A). Similarly, the ratio of the leg opposite to the angle, to the leg adjacent to the angle, CB/AC = C'B'/AC' = C"B"/AC" is a constant, called the tangent of the angle A, and written tan(A). These three functions can also be defined for zero, right, obtuse, and other angles using the diagram at the top of the following Web page from our Frequently Asked Questions (FAQ): Trigonometry Formulas http://mathforum.org/dr.math/faq/formulas/faq.trig.html - Doctor Rob, The Math Forum http://mathforum.org/dr.math/
Search the Dr. Math Library:
Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.