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This lesson focuses on finding slopes of parallel and perpendicular lines, as well as identifying the relationship between the slopes. Practice problems and interactive activities are included.
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Warm-up 1) Find the measure of angles a, b and c. 2) Find the slope between the points (-2, 8) and (14, 40)
Let’s look at the slopes of PARALLEL LINES • Use each side of your ruler to draw two parallel lines on your graph paper. • Find 2 points on each line (pick nice ones that lie on the cross of grid lines) • Figure out each path you’d have to walk if the boxes were city blocks between each pair of points. • Count the boxes you moved up or down, then count the boxes you moved left or right • Write it as a fraction • How do the slopes of each line compare?
Let’s look at the slopes of PERPENDICULAR LINES • Draw a line. Place your protractor on that line, and mark a point at the 90° point & where the vertex of the angle should be. • Draw a line through those two points. These lines are now perpendicular. • Find 2 points on each line (pick nice ones that lie on the cross of grid lines). • Figure out the path you’d have to walk if the boxes were city blocks on each line. • Count the boxes you moved up or down, then count the boxes you moved left or right • Write it as a fraction. • How do the slopes of each line compare?
Slope - The ratio of the vertical change to the horizontal change between two points on a line. (Rise over Run) Formula: m =
Practice Finding Slope • Find the slope of the line through (3, 2) and (-1, 6) • Find the slope of the line through (5, -1) and (2, -7) • Find the slope of the line through (2, -3) and (2, 8)
Horizontal Lines m =
Vertical Lines m =
Slopes of Parallel and Perpendicular Lines Parallel Lines – Slopes are the same Perpendicular Lines – Slopes are opposite reciprocals
Does order matter? Find the slope of the line passing through (7, 3) and (5, 9). Here is how they solved the problem: Jose Jeffrey Mike Maria
Does order matter? (7, 3) represents ( x1 , y1)(5, 9) represents ( x2 , y2) (7, 3) represents ( x2 , y2)(5, 9) represents ( x1 , y1) Jose Jeffrey Mike Maria (7, 3) represents ( x2 , y1)(5, 9) represents ( x1 , y2) (7, 3) represents ( x1 , y2)(5, 9) represents ( x2 , y1)
4) Find the slope of a line parallel to the line that passes through (2, 3) and (4, 7) • Find the slope of a line perpendicular to the line that passes through (-1, 0) and (4, 7) • Find the slope of the line through the points (7, 0) and (7, -3).
3 Point Quiz • Graph and find the slope of a line through the points A(-7, 5) and B(7, -5) • What is the slope of a line that is perpendicular to line AB?
Homework • p. 136, 1-6, 10
Pop Quiz Find the slope of the lines through the following two points: (2pts) (2, 8) and (-3, 15)
Let’s look at the slopes of PARALLEL LINES • Use each side of your ruler to draw two parallel lines on your graph paper. • Find 2 points on each line (pick nice ones that lie on the cross of grid lines) • Figure out each path you’d have to walk if the boxes were city blocks between each pair of points. • Count the boxes you moved up or down, then count the boxes you moved left or right • Write it as a fraction • How do the slopes of each line compare?
Let’s look at the slopes of PERPENDICULAR LINES • Draw a line. Place your protractor on that line, and mark a point at the 90° point & where the vertex of the angle should be. • Draw a line through those two points. These lines are now perpendicular. • Find 2 points on each line (pick nice ones that lie on the cross of grid lines). • Figure out the path you’d have to walk if the boxes were city blocks on each line. • Count the boxes you moved up or down, then count the boxes you moved left or right • Write it as a fraction. • How do the slopes of each line compare?
Slope - The ratio of the vertical change to the horizontal change between two points on a line. (Rise over Run) Formula: m =
Practice Finding Slope • Find the slope of the line through (3, 2) and (-1, 6) • Find the slope of the line through (5, -1) and (2, -7) • Find the slope of the line through (2, -3) and (2, 8)
Rules • Do what the slide says on your whiteboard. When a slide changes, rotate your whiteboard with your group. Do not erase your whiteboard unless the slide says to.