# Homework Help: Mathematical Economics, Minimization

1. Jul 27, 2009

### dracolnyte

1. The problem statement, all variables and given/known data
Consider the following general form of a constant elasticity of substitution production function:

y = [SLp + (1 - S)Kp]1/p

Assume a firm is trying to minimize the cost of producing any given y. Cost are given by

C = wL + rK

Find the firm's cost minimizing demand function for L. The cost minimizing demand for K is determined simultaneously, so you need both first order conditions. You may assume that nonneggativity constraints on L and K are not binding.

3. The attempt at a solution
Is y = [SLp + (1 - S)Kp]1/p expandable?

2. Jul 27, 2009

### Hurkyl

Staff Emeritus
Not in any pleasant fashion. Why would you want to expand it?

3. Jul 27, 2009

### dracolnyte

because my prof said it would be easier if we let a1 = S1/p and a2 = (1-S)1/p and leave our answers in terms of a1 and a2

4. Jul 27, 2009

### dracolnyte

im guessing i can make a1p = S and a2p = (1 - S)
then i would get

y = [a1pLp + a2pKp]1/p

y = [(a1L)p + (a2K)p]1/p

5. Jul 27, 2009

### Hurkyl

Staff Emeritus
This is certainly correct.

FYI, I don't think this change of variable has anything to do with how to go about performing this calculation -- it's just a little optional detail that may (or may not) make it less tedious.

6. Jul 27, 2009

### snipez90

Seems pretty standard. You want to minimize wL + rK over L and K, with y - [SLp + (1 - S)Kp]^1/p = 0 as your constraint. Define the lagrangian and derive the first order conditions by differentiating the lagrangian with respect to L, K, and lambda.