# Geometry: The Unit Circle and Trigonometry

## The Unit Circle and Trigonometry

Trigonometry is the study of triangles. You might be wondering why I would write a section about trigonometry and put it in a section about circles. The immediate answer that comes to mind is that I just now remembered to write it and stuck it in wherever it would fit. Although I have been accused of being an absent-minded professor, when it comes to the writing of this I have been on top of my game.

The reason that I am writing this section now is because so much about trigonometry has to do with circles! If I kept circles out of trigonometry, you wouldn't have the tools necessary to handle angles greater than 90. You'll see what I mean once you embed these triangles inside the unit circle.

You will embark on your trigonometric travels via right triangles. Be sure to pack along the Pythagorean Theorem (our currency of choice) and properties of proportionalities (to convert currencies). You will then come full circle when you re-examine these ideas through the eyes of the unit circle.

Excerpted from The Complete Idiot's Guide to Geometry 2004 by Denise Szecsei, Ph.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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