198 Chapter 3 Graphing Linear Equations in Two Variables Daily Low Temperatures (Fahrenheit) for Sudbury, Canada y 8 6 1 2 3 4 5 6 7 Temperature (F) 4 2 0 2 4 6 45 40 35 30 20 15 10 Section 3.1 Practice Exercises Day x Study Skills Exercise Before you proceed further in Chapter 3, make your test corrections for the Chapter 2 test. See the Study Skills Exercise in Section 2.1 for instructions. Vocabulary and Key Concepts 1. a. In a rectangular coordinate system, two number lines are drawn at right angles to each other.The horizontal line is called the -axis, and the vertical line is called the . b. A point in a rectangular coordinate system is defined by an pair, (x, y). c. In a rectangular coordinate system, the point where the x- and y-axes intersect is called the and is represented by the ordered pair . d. The x- and y-axes divide the coordinate plane into four regions called . e. A point with a positive x-coordinate and a y-coordinate is in Quadrant IV. f. In Quadrant , both the x- and y-coordinates are negative. Concept 1: Interpreting Graphs For Exercises 2–6, refer to the graphs to answer the questions. (See Example 1.) 2. The number of Botox injection procedures (in millions) in the United States over a 6-yr period is shown in the graph. a. For which year was the number of procedures the greatest? b. Approximately how many procedures were performed in year 5? c. Which year corresponds to 2.3 million procedures? 3.5 3 2.5 2 Number of Botox Procedures in the United States (in millions) 1.5 0 1 2 3 4 5 Number of Procedures (in millions) Year 1 0.5 0 b. Skill Practice 7. The table shows the number of homes sold in a certain town for a 6-month period. Plot the ordered pairs. Month, x Number Sold, y 1 20 2 25 3 28 4 40 5 45 6 30 Answer 7. 0 0 1 2 3 4 5 6 Number Sold Month 25 5 y x TIP: The graph in Example 4(b) shows only Quadrants I and IV because all x-coordinates are positive.
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