1. 3-6 Writing Equations of Parallel and Perpendicular Lines
LEQ: How do you write equations for lines that are parallel or perpendicular to a given line?

2. Parallel Slope Property:
Two nonvertical lines are parallel if and only if their slopes are equal.
Any 2 vertical lines are parallel.

3. Determining whether lines are parallel.
Are the lines in the figure below parallel? Explain.
Yes, b/c they both have the same slope.

4. What do you need in order to be able to write an equation of a line?
The slope of the line.
A point that the line goes through.

5. Writing an Equation of a Parallel Line.
Write an equation for a line that contains (- 2, 3) and is parallel to the graph of 5x – 2y = 8.
Step 1: Find the slope of your new line.

6. Step 2: Use your new slope and the given point to write an equation in point-slope form.

7. Perpendicular Slope Property:
Two nonvertical lines are perp. iff the product of their slopes is -1.
The slopes of 2 perp. lines are opposite reciprocals.
Any vertical and horizontal line are always perp.

8. Checking for Perpendicular Lines.
Prove that the lines in the figure below are perpendicular.
Blue Line:
m =
Red Line:

9. Writing an Equation of a Line Perpendicular to a Given Line.
Write the equation of the line that passes through the point (0, 4) and is perpendicular to y = 2x – 3.
Step 1: Find the slope of your new perp. line.

10. Step 2: Use your new slope and the given point to write your equation in point-slope form.

11. Closure: Describe the slopes of parallel lines.
Describe the slopes of perpendicular lines.

12. Homework:
Pg #s 2 – 30 even.
Pg #s 2 – 30 every other even.