Writing Equations From Graphs Slope-Intercept Form

Review Any linear equation can be written in slope-intercept form by solving for y and simplifying. In this form, you can immediately see the slope and y-intercept. Also, you can quickly graph a line when the equation is written in slope-intercept form.

Review of Graphing from Slope-Intercept Form Given the equation y = 3x – 1 y = 3x – 1 is in the form y = mx + b slope: m = 3 = y-intercept: b = –1 • Step 1 Plot (0, –1). • Step 2 Count 3 units up and 1 unit right and plot another point. Step 3 Draw the line connecting the two points.

Practice graphing from Slope-Intercept Form Given the equation y = -2x +3 y = -2x + 3 is in the form y = mx + b slope: m =- 2 = y-intercept: b = +3 • • Step 1 Plot (0, 3). Step 2 Count 2 units down and 1 unit right and plot another point. Step 3 Draw the line connecting the two points.

Writing Equations from Graphs Given the line write an equation in slope-intercept form Run = 3 Step 1 Find the y-intercept • Rise = 4 This point is ( 0, -2) so the y-intercept is -2 Step 2 Move up or down the line until you reach another coordinate intersection. • Step 3 Figure the rise and run from the y-intercept to the other point A rise of 4 and a run of 3 gives us a slope of 4/3 Step 4 Write the equation of the line with a slope of 4/3 and y-intercept of -2 In slope-intercept form y = mx + b

Writing Equations from Graphs Given the line write an equation in slope-intercept form Step 1 Find the y-intercept Rise = -3 • This point is ( 0, 2) so the y-intercept is + 2 Step 2 Move up or down the line until you reach another coordinate intersection. • Run = 1 Step 3 Figure the rise and run from the y-intercept to the other point A rise of -3 and a run of 1 gives us a slope of -3/1 or -3 Step 4 Write the equation of the line with a slope of -3 and y-intercept of +2

Now you try • • • • • • • • • • Y-int = -2 Slope = 6/-1 =-6 Y-int = 0 Slope = ½ or -1/-2 = ½ • • • • Y-int = 0 Slope = 1/1 =1 Y-int = -2 Slope = 0/1 =0 • • • • •

Now you try • • • • • • • • 2. 1. Y-int = 0 Slope = 4/3 3. 4. Y-int = none Slope = undefined • • •

Now you try • • • • • • • • 6. 5. Y-int = 2 Slope = 4/3 8. 7. Y-int = none Slope = undefined • • •