Slope-intercept Form for the Equation of a Line
If we take the equation of a line and solve it for y we get the slope-intercept form for the equation of a line.
Definition
Slope-Intercept Form for the Equation of a Line
The slope-intercept form for the equation of a line with slope m and
y-intercept (0, b) is: y = mx + b
Example 1
Find the equation of a line in slope-intercept form that has slope m = 2 and y-intercept (0,
-3).
Solution |
y = mx + b |
The point (0, -3) has the form (0, b). So, b is -3. |
Thus, replace m with 2 and b with -3. |
y = 2x - 3 |
The slope-intercept form for the equation of this line is
y = 2x - 3 |
Example 2
Write the equation 4x - 3y = 12 in slope-intercept form.
Solution |
4x - 3y |
= 12 |
Solve the given equation for y.
|
Subtract 4x from both sides. |
-3y |
= -4x + 12 |
Divide both sides by -3. |
|
|
Simplify. |
y |
|
So, the equation in slope-intercept form is
.
The slope of this line is
and the y-intercept is (0,
-4).
Example 3
Find the slope-intercept form for the equation of the line that passes
through the points (-6, 1) and (2, 5).Solution
First, we need to find the slope, m.
In the slope formula, let (x1, y1) = (-6, 1) and (x2, y2)
= (2, 5).
So, the slope is
.
Note:
You can use either point (x1, y1) and (x2, y2).
Next, use the point-slope formula.
|
y - y1 |
= m(x - x1) |
Let (x1, y1) = (-6, 1) and
|
y - 1 |
|
y - 1 |
|
Then, solve for y.
|
Distribute
on the right side.
|
y - 1 |
|
Add 1 to both sides. |
y |
|
So, the slope-intercept form for the equation
Note:
You can also write
in standard
form, Ax + By = C. To do this, subtract
from both sides to
get
Now, multiply both sides by 2 to get:
-x + 2y = 8
|