222 Chapter 3 Graphing Linear Equations in Two Variables Determining the Slope of a Vertical Line 12, 12 Example 4 Find the slope of the line passing through the points and (2, 4). Solution: Label the points. 12, 12 and 12, 42 1x1, y12 1x2, y22 m m y2 y1 x2 x1 5 0 142 112 122 122 Undefined 5 4 y 1 54 3 1 2 3 4 5 21 1 2 3 4 5 Apply the slope formula. Because the slope, m, is undefined, we expect the points to form a vertical line as shown in Figure 3-21. Skill Practice Find the slope of the line through the given points. 4. 15, 62 and 15, 22 Figure 3-21 x 3 2 (2, 4) (2, 1) Determine the Slope of a Horizontal Line 13.4, 22 13.5, 22 Example 5 Find the slope of the line passing through the points and . Solution: Label the points. Apply the slope formula. Simplify. 13.4, 22 and 13.5, 22 1x1, y12 1x2, y22 m y2 y1 x2 x1 122 122 13.52 13.42 2 2 3.5 3.4 0 6.9 0 Because the slope is 0, we expect the points to form a horizontal line, as shown in Figure 3-22. Answers 4. Undefined 5. 0 5 4 y 3 1 54 3 1 2 3 4 5 21 1 3 4 5 Figure 3-22 x 2 (3.5, 2) (3.4, 2) Skill Practice Find the slope of the line through the given points. 5. 13, 82 and 15, 82
miller_beginning_intermediate_algebra_4e_ch1_3
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