1. Equations from Graphs LF.2.AC.7: Write an equation given
Thursday, October 21
Equations from Graphs
LF.2.AC.7: Write an equation given
the graph of a line or the x- and y-intercepts.

2. Slope-Intercept Form
The basic slope-intercept form of an equation of a line is:
y = mx + b
where m is the slope and b is the y-intercept.
If you have the slope and the y-intercept, then it is easy to write the equation – just plug the numbers into the basic form.
For example, if m = ½ and b = -6, the equation is:
y = ½ x – 6
FHS
Slope of a Line

3. The Slope of a Line Find the equation of the line in the graph below:x y
First determine the y-intercept (where does it cross the y-axis).
Then determine the slope – use any two points on the line.
Plug the numbers into the basic form:
FHS
Slope of a Line

4. Finding the Equation of a Line
Determine the equations of these lines.
For AB:
For CD: x y C B D A
FHS
Slope of a Line

5. Using the x- and y-intercepts
Another way to graph a line from an equation is to find the x- and y-intercepts. x y
For the x-intercept, put a 0 into the equation in the place of y and solve for x:
For the y-intercept, put a 0 into the equation in the place of x and solve for y: :
FHS
Slope of a Line