4-3B Graphing Lines Using Slope Intercept Algebra 1 Glencoe McGraw-Hill Linda Stamper

Ax + By = C What is the standard form for a linear equation? The x-intercept and the y-intercept are numerical values. They are NOT __________. They are NOT _______. ordered pairs! equations! You can graph a line using one point, if you know it is a vertical or horizontal line! How can you tell by looking at the equation? Horizontal and vertical lines have only one variable in the equation!

In the previous chapter you graphed an equation using a table of values or by using the x and y intercepts. Today you will learn another method to graph an equation. This method uses the slope-intercept form. The linear equation y=mx+b is written in slope-intercept form where m is the slope and b is the y-intercept. y-intercept slope

Can you tell whether the graph will go uphill or downhill? Graph the equation y = –6x + 3. Can you tell whether the graph will go uphill or downhill? What clue tells you this will NOT graph as a vertical or horizontal line?

• • Graph the equation y = –6x + 3. 1. Plot the y-intercept. 2. Use slope to locate second point. x 3. Draw a line through the two points. • Copy the above 3 steps in your spiral notebook! How do you check if you have the correct graph? Using the coordinate of each point, substitute into the original equation. Does it produce true statements?

• • Graph the equation y = –6x + 3. coordinate for y-intercept ( , ) 3 • 3 = –6(0) + 3 3 = 0 + 3 x 3 = 3 • coordinate for other points y = –6x + 3 ( , ) 1 -3 -3 = –6(1) + 3 -3 = -6 + 3 -3 = -3 Using the coordinate of each point, substitute into the original equation. Does it produce true statements?

Example 1 Graph the equation y = –3x + 2. How do you know by looking at these equations, that they will NOT graph as horizontal or vertical lines?

Ex 1 y = –3x + 2. Ex 2 y = 4x – 5. • x x • • • Ex 3 Ex 4 • • x x • • y

How do you check if you have the correct graph? Write the equation in slope-intercept form. Then graph. The equation. Rewrite in slope-intercept form (solve for y). 1 y Graph. • • y-intercept is 3 • slope is 2 x How do you check if you have the correct graph? Using the coordinate of each point, substitute into the original equation. Does it produce true statements?

Write the equation in slope-intercept form. Then graph. Example 5 Example 6

How do you check if you have the correct graph? Example 5 Example 6 y-int. is –3 y-intercept is 2 slope is 5 Remember the negative can go in the numerator or denominator. • • • x • x How do you check if you have the correct graph? • Using the coordinate of each point, substitute into the original equation. Does it produce true statements? y y

Class Work Skills Practice Page 26.

Homework 4-A6 Page 208-209 # 24-32,48-58.

• • Example 1 Graph the equation y = –3x + 2. 1. Plot the y-intercept. 2. Use slope to locate second point. • x • 3. Draw a line through the two points.

• • Example 2 Graph the equation y = 4x – 5. 1. Plot the y-intercept. 2. Use slope to locate second point. x • 3. Draw a line through the two points. •

Assign the negative to the numerator or the denominator! Example 3 Graph the equation y 1. Plot the y-intercept. • 2. Use slope to locate second point. x • 3. Draw a line through the two points. Assign the negative to the numerator or the denominator!

Assign the negative to the numerator or the denominator! Example 4 Graph the equation y 1. Plot the y-intercept. 2. Use slope to locate second point. • x • 3. Draw a line through the two points. Assign the negative to the numerator or the denominator!