Page 95 - Math Course 3 (Book 1)

Rate of Change and Direct Variation

Use Graphs to Identify Proportional
Relationships
SHIPPING
The charge for shipping CDs from an Online store CDs Shipping($)
is based on the number of CDs in the package. 1 1.99
Determine if there is a proportional linear
relationship between the shipping charge 2 2.98
and the number of CDs.
3 3.97
A. Yes, since the number of CDs is proportional to
the shipping charge. 4 4.96

B. Yes, since the charge for each additional CD is
$0.99.

C. No, since the shipping charge is not
proportional to the number of CDs.

D. No, since the shipping charge is not equal to the
number of CDs.

Answer

MO. 3 - L4b constant of variation
In the equation y = kx, k is called the constant of
Solve Problems Involving variation or constant of proportionality.

Direct Variation k is constant (the

Vocabulary A-Z y = 2x same for every point)
constant of variation
Let us learn some vocabulary for y = 2x
y = 2x

y = kx
Direct variation

A special type of linear equation that describes
constant rate of change is called a direct Key Concept
variation. The graph of a direct variation always
passes through the origin and represents a
proportional linear relationship. Direction Variation

Graph of Direct Variation Words A direct variation is a relationship in which
y = 2x This line is a direct the ratio of y to x is a constant, k. We say
y varies directly with x.
variation because it
passes through the origin Symbols Model
y = kx y = kx, where k ≠ 0
y = 2x
slope Example
Origin y = 2x
(0, 0)
y - intercept is zero

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