英文的导数数学题,

题目

英文的导数数学题,
(1 pt) The total cost (in dollars) of producing coffee machines is
C(x)=1900+70x-0.7x^2
(A) Find the exact cost of producing the 21st machine.
Exact cost of 21st machine =
(B) Use marginal cost to approximate the cost of producing the 21st machine.
Approx.cost of 21st machine =

答案

(A)
Exact cost of 21st machine = C(21)-C(20)=3161.3-3120=41.3


(B)
MC(x)=70-1.4x
Approx.cost of 21st machine =MC(20)=70-1.4×20=42