Two quantities 
and 
exhibit direct variation if they are related by a nonzero constant
of variation 
such that
 |
Equivalently, 
for 
,
and 
is directly proportional to 
. Thus multiplying 
by a factor also multiplies 
by the same factor.
The function graph of a direct variation is a straight
line through the origin with
slope 
(OpenStax 2021).
