Two quantities 
and 
are said to be directly proportional, proportional, or "in direct proportion"
if 
is given by a constant multiple of 
, i.e., 
for 
a constant. This relationship is commonly written 
.
Directly Proportional
See also
Inversely Proportional, ProportionalExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Directly Proportional." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/DirectlyProportional.html