Section 3.3 Slope of a Line and Rate of Change 221 When you apply the slope formula, you will see that the slope of a line may be positive, negative, zero, or undefined. • Lines that increase, or rise, from left to right have a positive slope. • Lines that decrease, or fall, from left to right have a negative slope. • Horizontal lines have a slope of zero. • Vertical lines have an undefined slope. Finding the Slope of a Line Given Two Points 2. 15, 12 Find the slope of the line passing through the points and Solution: a5, and a2, b 3 2 (x1, y1) (x2, y2) Label the points. Apply the slope formula. Simplify. 2, 15, 12 By graphing the points and we can verify that the slope is (Figure 3-20). Notice that the line slopes downward from left to right. 5 4 y 1 252423 1 2 3 4 5 2221 21 22 23 24 25 Skill Practice Find the slope of the line through the given points. 3. and a 1 6 2 3 a , 0b , 5b 27 12, 32 2 2 7 or 2 7 4 2 2 5 m y2 y1 x2 x1 a 3 2 b a 1 2 b 122 152 1 2 b 12, 32 2 Example 3 Answer 3. 6 Positive Slope Negative Slope Zero Slope Undefined Slope Figure 3-20 x 3 2 7 2 (2, 2 ) 32 (25, ) 12 Avoiding Mistakes When applying the slope formula, y2 and x2 are taken from the same ordered pair. Likewise y1 and x1 are taken from the same ordered pair.
miller_beginning_intermediate_algebra_4e_ch1_3
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