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In this lesson, students learn to use slope-intercept form to graph a line. Slope-intercept form is y = mx + b form, where m represents the slope, and b represents the y-intercept. So if the equation of a line is y = 3/4 x - 2, then the line is written in slope intercept form, or y = mx + b form, with m = 3/4 and b = -2. To graph the line, start with the y-intercept, or b, of -2. From there, take the slope, or m, of 3/4, plot a second point, and graph the line.
To graph a line using slope intercept form that has an equation like y = -3x, change it to y = -3x + 0 so that it matches up with y = mx + b form. Its slope, therefore, is -3 (which can be thought of as -3/1), and its y-intercept is 0.
To graph a line using slope intercept form that has an equation like y = 4, think of it as y = 0x + 4. Its slope, therefore, is 0, and its y-intercept is 4, so its graph is a horizontal line up 4 units on the y-axis.
Slope intercept form makes it easy to graph a line quickly, without have to set up a chart and plug in values for x.
