7.01:_Introduction

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<p class="lt-math-9863">The word &ldquo;geometry&rdquo; comes from the ancient Greek words &ldquo;geo&rdquo; meaning Earth and &ldquo;metron&rdquo; meaning measurement. It is probably the oldest field of mathematics, because of its usefulness in calculating lengths, areas, and volumes of everyday objects.</p>

<p class="lt-math-9863">The study of geometry has evolved a great deal during the last 3,000 years or so. Like all of mathematics, what&rsquo;s really important in geometry is reasoning, making sense of problems, and justifying your solutions.</p>

<p class="lt-math-9863">The mathematician Henri Poincar&eacute; said that</p>

<blockquote>
<p class="lt-math-9863"><i>Geometry is the art of good reasoning from bad drawings.</i></p>
</blockquote>

<p class="lt-math-9863">This insight should guide your study in this chapter. You should never trust a drawing. You might find that one line segment appears to be longer than another, or an angle looks like it might be 90 degrees. But &ldquo;appears to be&rdquo; and &ldquo;looks like&rdquo; are simply not good enough. You have to reason through the situation and figure out what you know for sure and why you know it.</p>

<section class="box-exercise"><span id="Think_.2F_Pair_.2F_Share"></span><h2 class="box-legend lt-math-9863"><span class="lt-icon-default">Think / Pair / Share</span></h2>

<p class="lt-math-9863">Reflect on your learning of geometry in the past. What is geometry really about? Also think about these questions:</p>

<ul>
    <li class="lt-math-9863">What is a point?</li>
    <li class="lt-math-9863">What is a line? A segment? A ray?</li>
    <li class="lt-math-9863">What is a plane?</li>
    <li class="lt-math-9863">What is a circle?</li>
    <li class="lt-math-9863">What is an angle?</li>
    <li class="lt-math-9863">Which of these basic objects can be measured? How are they measured? What kinds of tools are useful?</li>
</ul>
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