Download Equation of a Line, Slope, and Y-intercept y = mx + b

Equation of a Line, Slope, and Y-intercept
y = mx + b
From Words
From An Equation
The interpretation of the words is very
important. You know that slope, m, is
the rate of change and that the yintercept, b, is the start amount.
Look for word phrases that indicated
change, such as, miles per hour, cost for
each class, etc. This indicates the rate.
If someone gives you the equation, then
you can use that equation to find the
slope and the intercept.
Look also for words that indicate the
start value. Birth, when started, etc.
This indicates the y-intercept.
Find these values and substitute into
the equation for a line
From A Table
From a Graph
Tables give us ordered pairs. If the
relationship is linear, then all you need
to do is to choose any two ordered pairs,
subtract the y values, subtract the x
values and write that as a
ratio(fraction). Remember to put the y
value on top. This is the slope.
If the table includes the value when
x = 0, then you have the y-intercept. If
not, then go down the table until you get
to x=0. This is the y intercept.
Place both of these values in the
equation for the line.
With a graph, you need to find the rise
and the run. You can do this by building
a right triangle on the graph and
counting the boxes or by reading the
ordered pairs and finding the change in
y and change in x as done in ‘From A
Table’
Find the y-intercept by finding the value
of y where the line crosses the y-anis.
This is b.
Examples
From Words
EX. There is 6inches of snow on the
ground. The weather man predicts ½ in
of snow fall per hour.
From a Table (with x = 0)
x
y
0
1
3
3
6
5
9
7
X
y
1
10
2
15
3
20
4
30
From an Equation
y = 2x + 5
From a Graph