Antiderivative of 1/((x(lnx)^3) using u-substitution

In summary, the student is trying to find the antiderivative of 1/((x(lnx)^3) using the substitution u=lnx. They are struggling with the third power in the problem, but after some clarification, they understand that the antiderivative is du/(u^3).
  • #1
stau40
37
0

Homework Statement


I'm working on an infinite series problem and need to find the antiderivative of 1/((x(lnx)^3).


Homework Equations


u=lnx


The Attempt at a Solution


I know I have to use the substitution u=lnx, but I still can't figure out what the answer is. I know the antiderivative of 1/((x(lnx)) is ln(lnx) but the third power in my problem is giving me trouble. Any advice? Thanks!
 
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  • #2
After the u-substitution, what is the integrand in terms of u now?
 
  • #3
It would be 1/(x(u)^3)
 
  • #4
stau40 said:
It would be 1/(x(u)^3)
When you make a substitution, replace everything. Here you still have a factor of x remaining. If u = ln(x), what is x in terms of u? Also, and this is related, did you replace dx by its appropriate expression involving du?
 
  • #5
Ok, it should be the antiderivative of du/(u^3) but I still don't understand how to work thru the third power. If I solve for the antiderivative and end up with u^4 I would need (1/4) in front of u and that gets me to the wrong result.
 
  • #6
stau40 said:
Ok, it should be the antiderivative of du/(u^3) but I still don't understand how to work thru the third power. If I solve for the antiderivative and end up with u^4 I would need (1/4) in front of u and that gets me to the wrong result.

Well, yes. You can't go from du/u^3 to u^4.

du/u^3 = u^(-3)du
 
  • #7
The light finally came on, Thanks!
 

FAQ: Antiderivative of 1/((x(lnx)^3) using u-substitution

1. What is an antiderivative?

An antiderivative is the inverse operation of a derivative. It is a function that, when differentiated, gives the original function.

2. What is the purpose of solving antiderivative problems?

Solving antiderivative problems helps us find the original function that was differentiated, which can be useful in a variety of applications such as physics, economics, and engineering.

3. How do you find the antiderivative of a function?

To find the antiderivative of a function, you can use the reverse power rule, integration by parts, or other integration techniques. It is important to remember to include the constant of integration when solving an antiderivative problem.

4. Are there any special cases when solving antiderivative problems?

Yes, there are some special cases when solving antiderivative problems. For example, some functions may not have an antiderivative that can be expressed in terms of elementary functions, and in these cases, we must use numerical methods to approximate the value of the antiderivative.

5. How can antiderivative problems be applied in real-life situations?

Antiderivatives have many practical applications, such as calculating displacement from velocity, finding the area under a curve, and determining the amount of work done by a force. They are also used in fields like economics to model changes in supply and demand.

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