Direct Variation
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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)

 


 
Topic Index | Algebra Index | Regents Exam Prep Center
Created by Michael Caldwell