Let 
 be the revenue for a production 
, 
 the cost, and 
 the profit. Then
and the marginal profit for the th unit is defined by
where ,
 
, and 
 are the derivatives of
 
, 
, and 
, respectively.
Let 
 be the revenue for a production 
, 
 the cost, and 
 the profit. Then
and the marginal profit for the th unit is defined by
where ,
 
, and 
 are the derivatives of
 
, 
, and 
, respectively.
Weisstein, Eric W. "Marginal Analysis." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/MarginalAnalysis.html