Calculating the Average Value of a Function Between Two Limits

Justabeginner
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Homework Statement


What is the average value of a function 1/x between x=2/3 and x=8/3?


Homework Equations


1/(b-a) ∫f(x) dx with a and b being the lower and upper limits, respectively


The Attempt at a Solution



1/([8/3] - [2/3])∫1/x dx
1/(6/3) ∫1/x dx
1/2 ∫1/x dx
1/2 * (ln x)

Plug in:
(ln {8/3})/2 - (ln {2/3}/2)
ln 4/2
ln 2

Is this correct? Thanks :)
 
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Justabeginner said:

Homework Statement


What is the average value of a function 1/x between x=2/3 and x=8/3?


Homework Equations


1/(b-a) ∫f(x) dx with a and b being the lower and upper limits, respectively


The Attempt at a Solution



1/([8/3] - [2/3])∫1/x dx
1/(6/3) ∫1/x dx
1/2 ∫1/x dx
1/2 * (ln x)

Plug in:
(ln {8/3})/2 - (ln {2/3}/2)
ln 4/2
ln 2

Is this correct? Thanks :)
Looks good.

Though, just to be clear, your reasoning for your last few steps was ##\frac{1}{2}\ln\left(\frac{(\frac{8}{3})}{(\frac{2}{3})}\right) = \frac{1}{2}\ln(4) = \ln(4^{\frac{1}{2}}) = \ln2##, correct?
 
Yes, that is exactly what I have written on my paper here. Thank you so much for your help :)
 
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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