Solving an Integral: My Struggle

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In summary, the conversation involved discussing the solution to an integral problem involving the function \frac{x\tan^{-1}x}{(1+x^2)^3}. The expert summarizer provided a summary of the steps taken to solve the integral, including the use of the substitution x = \tan{r} and the product rule. The conversation ended with the acknowledgement of the expert's genius and gratitude for their help.
  • #1
rocomath
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Integral: Hint please

[tex]\int\frac{x\tan^{-1}x}{(1+x^2)^3}dx[/tex]

[tex]\int\frac{\tan^{ - 1}x}{(1 + x^2)}\frac{x}{(1 + x^2)^2}dx\left\{\begin{array}{cc}x = \tan{r} \leftrightarrow r = \tan^{ - 1}x \\
dr = \frac {dx}{1 + x^2}\end{array}\right\}[/tex]

Let's not even get into what I did next and how much work I put into this Integral. This is definitely not the right way to go, hmm ...

Ok I think I see it now ... omg.
 
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  • #2
Well, therefore, you have:
[tex]\int\frac{x\tan^{-1}(x)}{(1+x^{2})^{2}}\frac{dx}{1+x^{2}}=\int\frac{\tan(r)r}{(1+\tan^{2}(r))^{2}}dr=\int\cos^{4}(r)\tan(r)rdr=\int{r}\cos^{3}(r)\sin(r)dr=\frac{1}{4}\int\cos^{4}(r)dr-\frac{r}{4}\cos^{4}(r)[/tex]

Agreed?
 
  • #3
On my previous try, after the 2nd to last step of yours, I did it differently; I would like to try your way, but I'm not sure what you did.

I did ... [tex]\int r\sin{r}(1-\sin^{2}r)\cos{r}dr[/tex]

Nvm, I see what you did. UHHH! I can't believe I spent more than an hour on this problem. Thanks arildno :-]
 
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  • #4
arildno said:
Well, therefore, you have:
[tex]\int\frac{x\tan^{-1}(x)}{(1+x^{2})^{2}}\frac{dx}{1+x^{2}}=\int\frac{\tan(r)r}{(1+\tan^{2}(r))^{2}}dr=\int\cos^{4}(r)\tan(r)rdr=\int{r}\cos^{3}(r)\sin(r)dr=\frac{1}{4}\int\cos^{4}(r)dr-\frac{r}{4}\cos^{4}(r)[/tex]

Agreed?

Hi arildno,

I followed all but how you went from the second last step to the last step, as there is an 'r' in the integrand. Are you using some sort of gamma function there. That's the closest I've seen to int( sin^m(x) x cos^n(x) dx)

Thanks.
 
  • #5
I'm just using the product rule:
[tex]u(r)=r, v'(r)=\cos^{3}(r)\sin(r)\to{v}(x)=-\frac{1}{4}\cos^{4}(r)[/tex]
 
  • #6
arildno said:
I'm just using the product rule:
[tex]u(r)=r, v'(r)=\cos^{3}(r)\sin(r)\to{v}(x)=-\frac{1}{4}\cos^{4}(r)[/tex]

You're a freakin genius. I totally didn't see that. I was trying to solve it using a gamma function. I think there should be something related to a gamma function too as you still have to solve the int(cos^4(r) dr) which is part of the question.

Thanks for the help.
 

FAQ: Solving an Integral: My Struggle

What is an integral and why is it important to solve?

An integral is a mathematical concept that represents the area under a curve on a graph. It is important to solve because it allows us to find the total amount or accumulation of a quantity over a given interval. It has many applications in fields such as physics, engineering, and economics.

What are the steps to solving an integral?

The first step is to identify the function to be integrated and the limits of integration. Then, use integration rules and techniques to rewrite the function in an integrable form. Next, evaluate the integral using either analytical or numerical methods. Finally, check the solution for accuracy by differentiating it.

What are some common challenges in solving integrals?

Some common challenges include identifying the appropriate integration rule or technique, dealing with complex or improper integrals, and determining the limits of integration. It can also be difficult to accurately evaluate the integral, especially when using numerical methods.

How can I improve my skills in solving integrals?

Practice is key when it comes to improving skills in solving integrals. Familiarize yourself with different integration rules and techniques and work through various examples. Additionally, understanding the concept behind integrals and how they relate to other mathematical concepts can also improve your skills.

Are there any resources available to help with solving integrals?

Yes, there are many resources available such as textbooks, online tutorials, and practice problems. You can also seek help from a math tutor or attend a workshop on solving integrals. Additionally, there are computer software programs that can assist in solving integrals.

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