# Optimization Problem, Laying down electrical lines (Multivariable)

1. Apr 21, 2013

### WalkTex

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

I am not really sure how to optimize it from here. What should I be taking the derivative of the price function with respect to ??

2. Apr 21, 2013

### Ray Vickson

Your total cost function C is a function of three variables (a,b,c). What do you know about optimizing multivariate functions? If your answer is that you don't know how to do it, then you need to do some reading; either look in a textbook, or search on-line (for example, by using Google search words 'multivariable optimization' or something similar).

3. Apr 21, 2013

### LCKurtz

How far to the right is the point Q from the point P? Perhaps it doesn't matter, but you need to limit a+b+c to some value to work the problem. So you have an additional equation a+b+c =D. That will let you express the total price in terms of two of the unknowns a,b,c. Differentiate with respect to them.