# Geometry For Dummies 3rd Edition

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## Book Preface

Geometry is a subject full of mathematical richness and beauty. The ancient Greeks were into it big-time, and it’s been a mainstay in secondary educa-tion for centuries. Today, no education is complete without at least some familiarity with the fundamental principles of geometry.
But geometry is also a subject that bewilders many students because it’s so unlike the math that they’ve done before. Geometry requires you to use deductive logic in formal proofs. This process involves a special type of verbal and mathematical reasoning that’s new to many students. Seeing where to go next in a proof — or even where to start — can be challenging. The subject also involves working with two- and three-dimensional shapes: knowing their properties, finding their areas and volumes, and picturing what they would look like when they’re moved around. This spatial reasoning element of geometry is another thing that makes it differ-ent and challenging.
Geometry For Dummies, 3rd Edition, can be a big help to you if you’ve hit the geom-etry wall. Or if you’re a first-time student of geometry, it can prevent you from hitting the wall in the first place. When the world of geometry opens up to you and things start to click, you may come to really appreciate this topic, which has fas-cinated people for millennia — and which continues to draw people to careers in art, engineering, architecture, city planning, photography, and computer anima-tion, among others. Oh boy, I bet you can hardly wait to get started!

Geometry For Dummies, 3rd Edition, covers all the principles and formulas you need to analyze two- and three-dimensional shapes, and it gives you the skills and strategies you need to write geometry proofs. These strategies can make all the difference in the world when it comes to constructing the somewhat peculiar type of logical argument required for proofs. The non-proof parts of the book contain helpful formulas and tips that you can use anytime you need to shape up your knowledge of shapes.
My approach throughout is to explain geometry in plain English with a minimum of technical jargon. Plain English suffices for geometry because its principles, for  the most part, are accessible with your common sense. I see no reason to obscure geometry concepts behind a lot of fancy-pants mathematical mumbo-jumbo. I prefer a street-smart approach.
This book, like all For Dummies books, is a reference, not a tutorial. The basic idea is that the chapters stand on their own as much as possible. So you don’t have to read this book cover to cover — although, of course, you might want to.

Conventions Used in This Book

Geometry For Dummies, 3rd Edition, follows certain conventions that keep the text consistent and oh-so-easy to follow:

» Variables are in italics.
» Important math terms are often in italics and are defined when necessary. Italics are also sometimes used for emphasis.
» Important terms may be bolded when they appear as keywords within a bulleted list. I also use bold for the instructions in many-step processes.
» As in most geometry books, figures are not necessarily drawn to scale — though most of them are.
» I give you game plans for many of the geometry proofs in the book. A game plan is not part of the formal solution to a proof; it’s just my way of showing you how to think through a proof. When I don’t give you a game plan, you may want to try to come up with one of your own.