Suppose that the total cost in dollars of producing x units of a product is given by
C(x) = 5,000 + 30xex/800.
Find the marginal cost when 800 units are produced
SOLUTION
The marginal cost when 800 units are produced is equal
to C' (800)
C'(x) = 30ex/800. + 30xex/800.( 1/ 800 )
Then C'(800) =$ 163.096 which is of course an approximation.
The actual cost for producing the 801st unit is C (801) -C( 800 ) =$70402.01 - $70238.76 = $163.25
The derivative as you see did a pretty good job