Page 324 - Algebra 1

You can use a graph to write an equation of the line in slope-intercept form.
Example
3
Writing the Equation of a Line from a Graph
a. Write the equation of the graphed line in slope-intercept form.
SOLUTION
Identify the y-intercept from the graph by identifying the y-value where the line crosses the y-axis.
y-intercept: -1
Identify the slope by determining how to move from one point
to another. rise = 1
2
Write the equation in slope-intercept form.
y = _1 x - 1 2
b. Write the equation of the graphed line in slope- intercept form.
SOLUTION
Identify the y-intercept from the graph by identifying the y-value where the line crosses the y-axis.
y-intercept: 2
Identify the slope by determining how to
move from one point to another.
rise = -3 run = 1 slope: -3
Write the equation in slope-intercept form. y = -3x + 2
Check Verifythesolutionbygraphingtheequation on a graphing calculator and comparing it to the original graph.
O
y
4
2
Rise
1
R
un
2
x
-4
-2
2
4
-2
y-intercept
run = 2 slope: _1
-4
y
y
-intercept
Rise -3
2
O
x
-4
-2
2
4
-2
Run 1
Math Reasoning
Generalize What is the slope of a horizontal line? What is the slope- intercept form of the equation of a horizontal line?
-4
Lesson 49 309