# 3 Slope intercept form

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```					SWBAT… Write lines in slope-intercept form   1/7/09

Agenda
1. WU (5 min)
2. Notes on slope intercept

Warm Up
What is the slope of the line passing through (-5,
2) and (6, 7) in the standard (x, y) coordinate
plane?

HW #2: Writing Equations in slope-intercept
Find the rate of change. Explain what
the rate of change means.

21
18
Points Scored

15
12
9
6
3
0
0   1         2       3        4       5    6   7
When an equation is in slope-intercept form:

Now look at the equation below……

y  2x  1
What is the slope? ____________

What is the y-intercept? ____________
• y = mx+ b is an equation that defines a line
• A line has two characteristics
– Points that fall on the line
– Slope
Converting linear
equations into Slope-
Intercept Form
Slope intercept form is:

y = mx + b
Our main goal is to get
the y alone on one side of
the equation
Class example - convert Into Slope-Intercept Form

2 y  4x  2
(divide both sides by 2 to get y alone)

2 y  4x  2
2        2
(now simplify all fractions)
2              1
2 y  4x  2
2    2    2
y  2x  1
*** Your turn - example 1 ***
Convert to Slope-Intercept Form:
5y = 10x + 15
(divide both sides by 5 to get y alone)
5 y  10 x  15
5        5
(now simplify all fractions)
5 y  10 x  15
5        5            5

y = 2x + 3 BRAVO!!
*** Your turn – example 2 – convert                to
Slope-Intercept Form ***

-3y = -9x - 12

Step 1: divide both sides by -3 to get y alone

Step 2: Simplify all fractions

Step 3: Write your equation in y = mx + b
What is the slope? ____________

What is the intercept? ____________

-3y = -9x - 12        (divide both sides by -3 to get y alone)

-3     -3
(now simplify all fractions)
-3y = -9x - 12
-3    -3 -3
y = 3x + 4
Slope = 3
Wow, you’re good
Intercept = 4        at this!!
***Class example***
Convert to Slope-Intercept Form:
21x – 7y =14     (subtract both sides by 21x)
21x           -21x
(now divide both sides by -7)
-7y = -21x + 14
7 - 7 -7               (simplify all fractions)

y = 3x – 2
***Final   Example - Your turn – example 3-Convert
to Slope-Intercept Form          ***
2y + 26 = -6x
Step 1: Subtract both sides by 26

Step 2: Divide both sides by 2 to get y by itself

Step 3: Simplify all fractions

What is the slope? ____________

What is the intercept? ____________
2y + 26 = -6x     (subtract both sides by 26)
26        -26
(now divide both sides by 2
2y = -6x - 26
2 2 2
(simplify all fractions)

y = -3x - 13
You are a math wizard!
Four students are renting a car for a road trip.
The cost of renting the car is given by the
function C = 12.5 + 21d, where C is the total
cost for renting the car for d days. What does
the slope of the function represent?
1.   number of people
2.   cost per day
3.   number of days
4.   miles per gallon
The cost of prints from an online photo
processor is given by C(p) = 29.99 +
0.13p. \$29.99 is the cost of membership,
and p is the number of 4-inch by 6-inch
prints. What does the slope represent?
1.   cost per print
2.   cost of the membership
3.   cost of the membership and 1 print
4.   number of prints

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