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4.5. Quick Graphing Using Slope-Intercept Form. What are the different methods we have used to graph a line?. Plot points. Make a table. Find the x and y- intercepts. Special horizontal and vertical lines. Slope-intercept form: linear equation. y = mx+b.
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4.5 Quick Graphing Using Slope-Intercept Form
What are the different methods we have used to graph a line? • Plot points • Make a table • Find the x and y- intercepts • Special horizontal and vertical lines
Slope-intercept form: linear equation y = mx+b m represents the slope of the line b represents the y-intercept *where the line crosses the y-axis
y = mx + b You can tell by looking at the equation not only where the line crosses y, but whether it has a positive or negative slope. If m is positive the slope is positive, and your line will go up from left to right. If m is negative, the slope is negative and your line will go down from left to right.
y = 3x + 4 y = ½ x – 9 y = -4/5 x + 7 y = -2x - 4 Slope= 3y-intercept = 4goes up left to right Slope = ½y-intercept = -9 goes up left to right Slope= -4/5y-intercept = 7 goes down left to right Slope= -2y-intercept = -4 goes down left to right Determine what is the slope,y-intercept, and direction of each equation.
When your equation is not in slope intercept form, rewrite it into slope-intercept form (y=mx+b). 2x = 5y - 10 • 2x = 5y-10-5y -5y • 2x – 5y = -10-2x -2x • -5y = -2x – 10-5 -5 -5 • y = 2/5x + 2 What is the y- intercept? 2 What is the slope? 2/5 What direction will the line go? Up, from left to right.
Graph the line y = 2/5x + 2The slope is 2/5 & the y-intercept is 2. • Steps to graphing a line in slope intercept form: • Plot the y-intercept. (0,2) • Count up 2 over 5 and plot next point. • Connect the dots. 4 3 2 1 -4 -3 -2 1 2 3 4 5 6 -1 -1 -2 -3 -4
Graph the line 2y = -2x + 6 4 • Change to slope intercept form. • y = -x + 3 • Y-intercept (0, 3) • Slope -1 • Line will go down from left to right. 3 2 1 -4 -3 -2 1 2 3 4 5 6 -1 -1 -2 -3 -4
Special line: • Parallel Lines: lines have the same slope, but different y-intercept (b value) • y = 2x + 4 and y = 2x – 3 are parallel lines.
Graph y = -x+6 and y = -x+2 on the same graph. Notice that they each have the same slope of -1, but they cross y at different spots.
y = -x + 6 y = -x + 2