3.4 Equations of Lines Then: You found the slopes of lines.

Now: 1. Write an equation of a line given information

about the graph.2. Solve problems by writing equations.

Review : Swim LessonsThe graph models the total

cost of joining a gym and taking swim lessons.

Slope of the graph is y = 15x + 20

1. What is the slope of this equation?2. What is the y-intercept?

3. What is the cost to join? Cost for 5 lessons?

Vocabulary:1. Slope- intercept form: y = mx + b where

m is the slope of the line andb is the y- intercept

2. Point-slope form: y – y1 = m(x – x1) where

(x1, y1) is any point on the line and

m is the slope of the line.

http://mathsongs.com/bookpix/cd7a.jpg

Example 1:Write an equation in

slope-intercept form of the line having a slope of 4 and y-intercept of 3. Then graph the line.

Equation:

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Example 2: Write an equation in

point-slope form of the line having a slope of 5 and contains (3, -2).

Then graph the line.

Equation:

Example 3:Write an equation of the line through each pair

of points in slope-intercept form.(0,-1) and (4,4)

1. Find the slope -

2. Use Point slope form to find equation-

Horizontal and Vertical Line Equations

1. Equation of horizontal line: y = b, where b is the y-intercept of the line

y = ________2. Equation of vertical

line: x = a, where a is the x-intercept of the line.

x = _________ https://share.ehs.uen.org/sites/default/files/images/grid%20of%205%27s.png

Example 4:Write an equation of the line through each pair

of points in slope-intercept form.

a. (-1, -4), (3,-4)Slope =

b. (-3, -2), (-3, 4)Slope =

3.4 AssignmentDay 1:

p. 202-203 #14-32 Evens, 42 a-cgraph 14, 20, 22 graph #42 on large paper with x

and y axis

Example 5: Write an equation in slope-intercept form for the line described.a. Passes through the point (2,0) and is perpendicular

to the line y = x + 2.1. New slope =2. Use Point-Slope form:

Example 5: Write an equation in slope-intercept form

for the line described.b. Passes through the point (-3,6) and is parallel

to the line y = - x + 3. 1. New slope =2. Use Point-Slope form:

Example 6: Rental CostsAn apartment complex charges $525 per month

plus a $750 annual maintenance fee.

a. Write an equation to represent the total first year’s

cost A for r months of rent.

Example 6 cont.b. Compare this rental cost to a complex which charges $200 annual maintenance fee but $600 per month for rent.

If a person expects to stay in an apartment for one

year, which complex offers the better rate?

3.4 Assignment:Day 2:pages 203-205

#37-40, 43-53,55, 60-63, 70-73