1. Drill #19
Determine the value of r so that a line through the points has the given slope:
1. ( 2 , r ) , ( -1 , 2 ) m = -½
Find the slope of the following lines. Determine whether they are parallel, perpendicular, or neither:
2. y = 3x – x + 2y = 6
y = -3x x = 1 – 6y

2. Drill #20 Find the slope intercept form of the following lines:
1. x + 2y = x + ½ y = 9
3. Find the slope intercept form of the line passing through (1, 3) with a slope of 2.
(Write the equation in point-slope for and solve for y.)

3. Drill #21 Identify which of the following lines are parallel:
1. x + 2y = 6 y = - ½x + 2
4y = 3 – 2x 4x - 8y = -10
2. Write an equation in slope intercept form parallel to y = 2x – 1 and passing through the point (1, 2).
3. Write an equation in slope intercept form perpendicular to 3x – 2y = 3 and passing through the point (3, -2).

4. Drill #23
Find the slope of the following lines and then determine which are parallel:
1. y = 2x + 3 y – 3 = 3(x + 1)
2x – y = 1 3y = 6x + 4
y = 3 y = ¾
2. Write an equation in slope intercept form parallel to
y = ½ x – 1 and passing through the point (4, 6).
3. Write an equation in slope intercept form perpendicular to y = ½ x – 1 and passing through the point (4, 6).

5. 2-4 Writing Linear Equations
Objective: To write an equation of a line in slope intercept form given the slope and one or two points, and to write an equation of a line that is parallel or perpendicular to the graph of a given equation.

6. Slope-Intercept Form Definition: An equation in the form of y = mx + b
where m = slope and b = y- intercept
In order to write an equation in slope-intercept form you need to know the slope (m) and the y- intercept (b)

7. Classwork Use the Standard Form formulas: Y-intercept = C/B
Slope = -A/B
To complete
2-4 Practice #1-4

8. Classwork
2-4 Practice
#9 – 17 (ODD)

9. Writing Equations in Slope Intercept Form*
Write the equation of the line with given slope and y- intercepts:
Ex1: m = 5 b = ¾
1A: m = b =
1B: m = 0 b = 0

10. Point Slope Form * Point Slope Form: An equation in the form of where
Are the coordinates of a point on the line and m is the slope of the line.
NOTE: For point slope form we need a point and the slope (or two points).

11. Point Slope Examples
Find the equation of the line (in point-slope form):
Ex2. m = 2 and passes through (2, -3)
2A. m = ½ and passes through (-2, 5)

12. Find the Equation of a Line in Slope Intercept Form*
Passing through a point (x1, y1) with slope m:
Method 1:
1. Substitute the point (x1, y1) and the slope m into the formula y = mx + b
2. Solve for b.
3. Substitute m and b into y = mx + b formula
Method 2:
1. Write the equation in Point Slope form.
2. Solve for y

13. Finding the equation of a line
Find the slope-intercept form of a line that has a slope of and passes through (-6, 1).
m = ?
b = ?
Method 1
Substitute m into the equation y = mx + b.
Substitute (-6, 1) for x and y in the equation.
Solve for b.
Once you know m and b you can put the equation in slope-intercept form.

14. Method 2: Point Slope to Slope Intecept
Convert the point-slope equation into slope-intercept.
To convert to slope-intercept form, solve the equation for y.

15. Classwork
2-4 Practice
#9 – 17 (ODD)

16. Write the Equation of a Parallel or Perpendicular Line*
1st Determine the slope of the line.
If finding a parallel line use the same slope as the line
If finding a perpendicular line use the negative reciprocal slope
2nd Write the equation in Point Slope form
3rd Convert to Standard or Slope-Intercept Form

17. Find the equation of the line* EXAMPLE 1
That passes through (-9, 5) and is perpendicular to the line whose equation is
y = -3x + 2
Find the perpendicular slope
Use the point (point- slope form) to find the equation of the line

18. Parallel/Perpendicular Examples
Find the equation of the line (in slope-intercept form):
1A. Parallel to y = 3x – 1 and passes through (2, -3)
1B. Perpendicular to 2x – y = 10 and passing through (-1, -2)