Consider a firm which faces the following production function:
Q = F(K, L)
where Q is the firm's output, K is the firm's capital input, and L is the firm's labor input.
This production function is assumed to have the following properties:
FK > 0, FL > 0, FKK < 0, FLL < 0, FKL = FLK < 0, and FKK * FLL > FKL^2.
Given (1), the firm's total revenue R is given by:
R = PQ = PF(K, L)
where P is the price of the firm's output (assume that P > 0), and the firm's cost C is given by:
C = rK + wL
where r is the interest rate, w is the wage, and C is the total cost.
Given (3) and (4), the firm's profit function can be written as follows:
̴̵̶̷̸̡̢̧̨̛̖̗̘̙̜̝̞̟̠̣̤̥̦̩̪̫̬̭̮̯̰̱̲̳̹̺̻̼͇͈͉͍͎̀́̂̃̄̅̆̇̈̉̐̑̒̓̔̽̾̿̀́͂̓̈́͆͊͋͌̕̚ͅ͏͓͔͕͖͙͚͐͑͒͗͛ͣͤͥͦͧͨͩͪͫͬͭͮͯ͘͜͟͢͝͞͠͡π = PF(K, L) - rK - wL
where π is the firm's profit. If the firm operates under perfect competition, the prices of output and inputs (P, r and w) are exogenous, and this implies that the firm chooses K and L which maximize π.
Given this firm's profit-maximizing problem, answer the following questions:
a) Obtain the FOC, πK = 0, which is expressed in terms of r (i.e. r is a function of other variables).
b) Obtain the FOC, πL = 0, which is expressed in terms of w (i.e. w is a function of other variables).
c) Obtain the SOC for maximum.
From your answers in a) and b), there exist i) a value of K and ii) a value of L which optimize π; let them be denoted by K* and L*, respectively.
Since the production function is stated in the general form, however, K* and L* cannot be derived explicitly. To get around this problem, let's assume a specific, Cobb-Douglas production function as follows:
Q = K^1/3L^2/3
Then, the profit function becomes:
π = PK^1/3L^2/3 - rK - wL