Exercise 20 Page 80

Can you think of two different ways to find the slope, given a graph?

- 6

Practice makes perfect

Observing the given graph, we can see that the line passes through the points (4,20) and (6,8). One way to use a graph to find the slope of a line is to count out the change in x and y.

We can see that as the graph travels from left to right, the rise, or change in y, is - 12. Similarly, the run, or change in x, is 2. slope=rise/run ⇔ m=- 12/2=- 6 We can confirm this answer by using the other method, the Slope Formula. m = y_2-y_1/x_2-x_1 We will use the given points to solve for the slope.

m = y_2-y_1/x_2-x_1

SubstitutePoints

Substitute ( 4,20) & ( 6,8)

m=8- 20/6- 4

SubTerms

Subtract terms

m=- 12/2

CalcQuot

Calculate quotient

m=- 6

A slope of m=- 6 means that for every 1 step in the positive horizontal direction, the graph travels 6 steps in the negative vertical direction.