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Big Ideas Math: Modeling Real Life, Grade 8

BI

Big Ideas Math: Modeling Real Life, Grade 8 View details

Cumulative Practice

Exercise 1 Page 313

Given a graph, can you think of two different ways to find the slope?

B

Observing the given graph, we can see that the line passes through the points (-4,5) and (1,- 3). 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 - 8. Similarly, the run, or change in x, is 5. slope=rise/run ⇔ m=-8/5=- 8/5 We can confirm this answer by using 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 ( -4,5) & ( 1,-3)

m=- 3- 5/1-( - 4)

a-(- b)=a+b

m=- 3-5/1+4

Add and subtract terms

m=- 8/5

MoveNegNumToFrac

Put minus sign in front of fraction

m=-8/5

We obtained the same number as before. We can be sure the slope is - 85. Therefore, the correct option is B.

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