3 5 Slopesofof Lines Warm Up Lesson Presentation

3 -5 Slopesofof. Lines Warm Up Lesson Presentation Lesson Quiz Holt Geometry Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Warm Up Find the value of m. 1. 2. 3. 4. undefined Holt Mc. Dougal Geometry 0

3 -5 Slopes of Lines Objectives Find the slope of a line. Use slopes to identify parallel and perpendicular lines. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines The slope of a line in a coordinate plane is a number that describes the steepness of the line. Any two points on a line can be used to determine the slope. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Example 1 A: Finding the Slope of a Line Use the slope formula to determine the slope of each line. AB Substitute (– 2, 7) for (x 1, y 1) and (3, 7) for (x 2, y 2) in the slope formula and then simplify. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Check It Out! Example 1 Use the slope formula to determine the slope of JK through J(3, 1) and K(2, – 1). Substitute (3, 1) for (x 1, y 1) and (2, – 1) for (x 2, y 2) in the slope formula and then simplify. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines One interpretation of slope is a rate of change. If y represents miles traveled and x represents time in hours, the slope gives the rate of change in miles per hour. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Example 2: Transportation Application Justin is driving from home to his college dormitory. At 4: 00 p. m. , he is 260 miles from home. At 7: 00 p. m. , he is 455 miles from home. Graph the line that represents Justin’s distance from home at a given time. Find and interpret the slope of the line. Use the points (4, 260) and (7, 455) to graph the line and find the slope. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Example 2 Continued The slope is 65, which means Justin is traveling at an average of 65 miles per hour. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Holt Mc. Dougal Geometry

3 -5 Slopes of Lines If a line has a slope of perpendicular line is The ratios Holt Mc. Dougal Geometry and , then the slope of a. are called opposite reciprocals.

3 -5 Slopes of Lines Example 3 A: Determining Whether Lines Are Parallel, Perpendicular, or Neither Graph each pair of lines. Use their slopes to determine whether they are parallel, perpendicular, or neither. UV and XY for U(0, 2), V(– 1, – 1), X(3, 1), and Y(– 3, 3) The products of the slopes is – 1, so the lines are perpendicular. Holt Mc. Dougal Geometry

3 -5 Slopes of Lines Example 3 C: Determining Whether Lines Are Parallel, Perpendicular, or Neither Graph each pair of lines. Use their slopes to determine whether they are parallel, perpendicular, or neither. CD and EF for C(– 1, – 3), D(1, 1), E(– 1, 1), and F(0, 3) The lines have the same slope, so they are parallel. Holt Mc. Dougal Geometry