EXAMPLE 2 How many different rays, line segments, and lines are represented in this example? Name each of the numbered angles in this fi gure in two different ways. P Y X 4 3 1 2 Q Z Solution First, notice that X is the vertex of all the angles. So, we cannot use just the vertex to name any of the angles in this fi gure. We can give each of the angles the following names: 1: YXZ or ZXY 2: ZXQ or QXZ 3: PXQ or QXP 4: PXY or YXP YOU TRY 2 Name each of the numbered angles in this fi gure in two different ways. M Q N 2 P 4 3 R 1 Angles can be different sizes. In Example 2, 1 is smaller than 2. We can measure the size of an angle using degrees. The symbol for degrees is . For example, if the measure of an angle is 45 degrees, we write 45. Let’s look at a circle to understand the sizes of degree measures. If we start at a ray and go all the way around the circle, we have moved 360. We say that a circle contains 360. If we start at a ray and form an angle halfway around a circle, the angle measure is 180. A straight angle is an angle whose measure is 180. The angle formed by moving a quarter of the way around a circle has a measure of 90. A right angle is an angle whose measure is 90. (It may also be called a square angle.) A right angle is denoted with a small square at the vertex: A right angle has a measure of 90°. 360° 180° 90° www.mhhe.com/messersmith SECTION 4.1 Introduction to Geometry 287
messersmith_power_prealgebra_1e_ch4_7_10
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