LESSON 8 SESSION 2
Name
Practice Showing That the
Slope of a Line Is Constant
> Study the Example showing that the slope of a
line is constant. Then solve problems 1-5.
Example
Cece draws a graph representing her
family's car trip to the beach. She wants
to show her father that their gas
mileage in miles per gallon was the
same for the entire trip. Cece chose
three points on the line and drew
vertical line segments from the points to
the x-axis. How can she use these
segments to prove that the gas mileage
was constant for the trip?
Distance (mi)
250
150
100
30
0
(S. 155)
(1,31)
8 10
What was the gas mileage for the trip in the Example?
6
Gasoline Used (gal)
The vertical line segments create three
similar right triangles. Because the
triangles are similar, the quotient of the length of the vertical side to the length
of the horizontal side is the same for each triangle. These quotients are slopes
between (0, 0) and the points Cece chose. Because Cece could have chosen any
points on the line to make the similar triangles, the slope is constant for the
whole line. So, the gas mileage is constant for the whole trip
For the graph in the Example, find the slope between the origin and each of the
points Cece chose.
Vocabul
slope
for any two
a line, the
shange
change
of