Slope-Intercept Form

One of the most common ways that the equations of lines are given is called slope-intercept form.  In order to write the equation of a line in slope-intercept form, you must know the slope and y-intercept of the line.

Example:

Recall that the y-intercept is the point where the graph crosses the y-axis. 

In this example, the y-intercept is 1.  Referring to the box above, you know that b is the y-intercept, so b = 1.

Next, look for two points on the graph that are easy to find, as you did in the last section.  Let’s use (-1, -1) and (0, 1).  The slope for the line is 2, so m = 2.

Plugging b and m into our general equation gives:

y = 2x + 1