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## Welcome! September 20 , 2010

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**Welcome!September 20, 2010**Take out: Pencil & journal Homework: • Objectives: • Students will determine the relationship between points and slope • Students will explore how scale changes a graph • Students will discover how to write the equation for a line Do Now: • Do Now • Do work in your Notes When you are done writing, put your pencil down and silently look up. Agenda: • Do Now • HW Check • Intro to Slope Formula • Modeling Problem • Work on class activity • Ticket to Go**(4, 1)**(-2, -2) Assuming each line is one unit, how many ways can we find the slope of this line?**Could these two lines have the same slope? How?**Complete in pairs p30, psD #1 (10 minutes)**Graph and find the slope given the points**1. (-3, 4) and (-7, 2) 2. (2, 4) and (3, 3) 3. (3, 5) and (4, 5) 4. (-3, 4) and (-4, 6) Two of the lines have negative slope, what do you notice about these lines? One of the lines has a slope of 0. What do you notice about that line? IS THERE A BETTER WAY TO FIND SLOPE???**FORMULA FOR FINDING SLOPE**The formula is used when you know two points of a line. EXAMPLE**Find the slope of the line between the two points (-4, 8)**and (10, -4) If it helps label the points. Then use the formula**Vocabulary**The equation for a line is often written in the form: y = mx + b, where m = slope and b = y-intercept. This is called Slope-Intercept form. Coefficient The multiplier of a variable Example: y = 2x + 3, 2 is the coefficient of x y-intercept The y-coordinate of the point at which the line crosses (or intercepts) the y-axis What is the y-intercept for y = 2x + 3? How about y = 3x - 4? How do you know?**Write the Equation**If a line has a slope of 3 and passes through the point (2, 5). Since slope = 3, we can replace m in y=mx+b with y=3x+b Now, replace x and y with 2 and 5, respectively giving you 5=3(2) + b Simplify, and you get b = -1 So, the equation for the line is: y = 3x -1**Find the line using the given**Slope 4 and passes through (1, 5) Slope -2 and passes through (8, -12) Slope 0 and passes through (3, 5) If you finish early, graph each equation.**Here’s a Challenge!**How could you find the equation for a line using just two points? Try with the following points (3, 7) and (8, 12) (6, 11) and (18, 17) (0, 0) and (100, 100) (3, 5) and (-1, 5)**Ticket to GO!**Find the equation for the line with slope 2/3 that passes through the point (9, 9)