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 – 4 3. 3x + 2y = 6y = -3x + 1 4x = 1 – 6y

Drill #20

Find the slope intercept form of the following lines:

1. x + 2y = 6 2. 3x + 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.)

Drill #21Identify 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).

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 + 4y = 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).

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.

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)

Classwork

Use the Standard Form formulas:

Y-intercept = C/B

Slope = -A/B

To complete

2-4 Practice #1-4

Classwork

2-4 Practice

#9 – 17 (ODD)

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

9

5

13

6

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 xxmyy ),( 11 yx

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)

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

Finding the equation of a lineFind 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.

3

2

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.

Classwork

2-4 Practice

#9 – 17 (ODD)

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

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

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)