Quick help with average value function problem please

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Discussion Overview

The discussion revolves around finding the average value function of the polynomial \( f(x) = (3x+5)^5 \) over the interval [1, 2]. Participants explore methods for calculating the integral and express uncertainty about the material covered in their course.

Discussion Character

  • Homework-related, Mathematical reasoning, Technical explanation

Main Points Raised

  • One participant initially presents the problem and expresses urgency and confusion about finding the average value function.
  • Another participant questions the method for finding the average value, prompting further discussion.
  • A correction is made regarding the function's power, changing it from \( (3x+5)^2 \) to \( (3x+5)^5 \).
  • Participants discuss the formula for the average value, noting the integral from 1 to 2 of the function divided by the length of the interval.
  • There is a suggestion that the problem may involve substitution, with one participant proposing \( t = 3x + 5 \) as a substitution method.
  • One participant expresses uncertainty about handling the integral of \( t^5 \) but indicates they have encountered similar problems before.
  • Another participant provides a step-by-step approach to solving the integral using the substitution method, leading to a new integral expression.
  • There is a discussion about whether the formula initially presented is applicable, with references to different types of problems in the textbook.
  • One participant reflects on the explanation provided and expresses confidence in proceeding with the problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method to solve the problem, with some expressing uncertainty about the material and others offering different approaches. The discussion remains unresolved regarding the best method to apply.

Contextual Notes

Participants indicate that they have not covered this material in class, leading to uncertainty about the steps involved in solving the integral and applying the average value formula.

c19dale
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I am in a time crunch and I am stumped...

I need to find the average value function of f(x) = (3x+5)^2 on [1, 2]


help please..
 
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What would you suppose to be the method of finding it out?
 
.

ok..i typed the problem wrong...its (3x+5)^5


I know the formula is 1/b-a int from 1 to 2 f(X)dx

but We haven't gone over this along with 4 other different problems I have left...I don't know how to handle the 5th power?
 
You'd know how to handle the integral [tex]\int_{1}^{2}t^{5}dt[/tex]

Right?
 
i think I could figure it out...we haven't gone over this material because we ran out of time...but I have figured out problems similar to that...
 
is this a substitution problem?
 
Allright:
If I asked you to find:
[tex]\frac{d}{dt}\frac{1}{6}t^{6}[/tex]
I hope you agree with me that we have:
[tex]\frac{d}{dt}\frac{1}{6}t^{6}=t^{5}[/tex]

Hence, to solve the problem:
1) Make a variable substitution (you've done this type of stuff, right?): t=3x+5
2) since t=8 when x=1 and t=11 when x=2, we get the integral:
[tex]\frac{1}{3}\int_{8}^{11}t^{5}dt[/tex]
which is the average value you're seeking.
 
no...I haven't done this stuff, but with what you just posted, I might be able to figure it out...thanks, I'll try it again...
 
so I don't use the formula I posted above?..I am just looking in the book, its a different type of problem(polynomial), but it gets a constant as the answer and it uses a formula to get it...
 
Last edited:
  • #10
c19dale said:
ok..i typed the problem wrong...its (3x+5)^5


I know the formula is 1/b-a int from 1 to 2 f(X)dx
This is certainly the formula I've used:
Since 2-1=1, we have:
[tex]\hat{f}=\frac{1}{1}\int_{1}^{2}(3x+5)^{5}dx=\int_{1}^{2}(3x+5)^{5}dx=\int_{8}^{11}\frac{1}{3}t^{5}dt[/tex]
 
  • #11
thats what I got after you explained it before, but does it simplify from there or is that the answer? ..never mind...i see...sub back in the value of t and solve...thanks, I got it...
 

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