Use marginal cost to estimate the cost of producing the 21st
     Use marginal cost to estimate the cost of producing the 21^st unit. x_0 =20  C (x) = 1/4 x^2 + 43 C\'(x) = 1/2 x Delta C = C\'(x_0)(Delta x)  What is the actual cost of producing the 21^st unit?  The demand function for a product is D (p) = squareroot 350-0.03p^2. (p-price) {3.4} Calculate the price elasticity of demand for this product. epsilon (p) = (-p) D \'(p)/D (p) 
  
  Solution
D(p)=sqrt(350-0.03p2)
D\'(p)=-.03 p/(sqrt(350-0.03p2))
Elasticity=(-p)D\'(p)/D(p)
= -p * (.03 p/sqrt(350-.03p2))* (1/sqrt(350-.03p2)) = .03p2/(350-.03p2)

