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When two variable quantities have a
constant (unchanged) ratio,
their relationship is called a direct
variation.
It is said that one variable "varies directly" as the
other.
The constant
ratio is called the constant of variation.
The formula for
direct variation is y = kx,
where k
is the constant of variation.
"y varies directly as x"
Solving for k:
(y =
numerator; x = denominator)
In a direct variation, the two
variables
change in the same sense. If one increases, so does the other.
Graphically, direct variation y
= kx when k > 0.
As x increases, y increases.
Example:
The weekly salary a woman earns, S, varies directly as the number of
hours, h, which she works. Express this relation as a formula.
Answer:
S =
hk
or
(where k
is the constant)
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