To write the equation of a line in slope-intercept form requires knowing the slope of a line and its y-intercept.

slope-intercept form: y = mx +b

Example 1:

Write the equation of the line whose slope is -4 and whose y-intercept is 3. Write the equation in slope-intercept form.

Solution:

The slope is given, so m = -4. The y-intercept is given, so b = 3. Substitute for m and b in the equation.

y = mx + b

y = -4x + 3

The slope-intercept form of the equation of the line described is

y = -4x + 3.

Example 2:

Write the equation of the line shown in the graph. Write the equation in slope-intercept form.

Solution:

The line intersects the y-axis at the point (0, -2), so the y-intercept b is -2. The line also passes through the point (2, 1). Use the two points to find the slope of the line. Let (X1, Y1) = (0, -2) and (X2, Y2) = (2, 1).

Knowing the slope, m=3/2 and the y-intercept, b=-2, you can write the equation of the line in slope-intercept form by substituting these values into the equation.

Assignment:

Write the equation of each line in slope-intercept form.

1. The slope is 4; the y-intercept is 3.

2. The slope is -2; the y-intercept is 6.

3. The slope is 1; the y-intercept is -4.

4. The slope is 1/2; the y-intercept is -3.

5. The slope is -2/3; the y-intercept is 1/2.

Write the equation of each line shown in the graph in slope-intercept form.

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