Max and min problem with 3 unknowns

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Hi,

I have this question for a college assignment. It involves 3 'unknowns' (not 3 variables, since 2 are constants). The main difficulty I am having is inexperience with max and min problems where you cannot fully evalaute the solution.

I think I have made a reasonable attempt at a solution, I would appreciate it if someone would take a brief look tell me what you think.


Thanks!


Homework Statement



Find V for maximum E, hence find E_max.

u and \theta are constants.

Homework Equations



Product rule: \frac{dy}{dx}=u\frac{dv}{dx}+v\frac{du}{dx}

The Attempt at a Solution

 
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Looks fine to me (although I just skimmed some of the algebra). Do you know yet if it's the correct answer?
 
berkeman said:
Looks fine to me (although I just skimmed some of the algebra). Do you know yet if it's the correct answer?


Hi, thanks for taking a look at my question.

The whole assignment isn't due for a week or so yet, so I won't find out for a while.

I am somewhat confident of my approach but was just wanting someone to look it over.


Cheers!
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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