Integrating tan^5(x)

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In summary, the homework statement is that integrating tan^5(x) gives the result -log(cos(x)). The Attempt at a Solution is that first, the problem can be broken down into (3+2) and then using the trig identity for tan squared, the left integral is easy to solve. The second integral is from several steps earlier and is also easy to solve. The final answer is -log(cos(x)).
  • #1
tangibleLime
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Integrating tan^5(x)... [UNSOLVED]

Homework Statement


[tex]\int tan^5(x) dx[/tex]


Homework Equations


[tex]tan^2(x) = sec^2(x) - 1[/tex]


The Attempt at a Solution



First I split it up into (3+2).
[tex]\int tan^3(x)tan^2(x) dx[/tex]

Using the identity for tangent squared...
[tex]\int tan^3(x)(sec^2(x) - 1) dx[/tex]

Distributing the tan cubed...
[tex]\int tan^3(x)sec^2(x)-tan^3(x) dx[/tex]

Braking it into two integrals...
[tex]\int tan^3(x)sec^2(x) dx - \int tan^3(x) dx[/tex]

For the first integral, substituting u = tanx, du = sec^2(x) dx which takes care of the right half of it.
[tex]\int u^3 du = \frac{u^4}{4} = \frac{tan^4(x)}{4}[/tex]

Now for the second integral from several steps above. Breaking it down to take out a tangent to get a tan squared.
[tex]\int tan^2(x)tan(x) dx[/tex]

Using the trig identity for tan squared...
[tex]\int (sec^2(x)-1)tan(x) dx[/tex]

Distribute the tan...
[tex]\int sec^2(x)tan(x)-tan(x) dx[/tex]

Break this into another two integrals...
[tex]\int sec^2(x)tan(x) dx - \int tan(x) dx[/tex]

First off, the right integral is easy, so just do that first...
[tex]\int tan(x) dx = ln|sec(x)|[/tex]

Now substitute u = tanx for the left integral so du = sec^2(x) and take care of that secant squared.
[tex]\int u du = \frac{u^2}{2} = \frac{tan^2}{2}[/tex]

Combining these last two results (the right integral on the first separation way in the beginning)
[tex]\frac{1}{2}tan^2(x) - ln|sec(x)|[/tex]

Combining it with the original left integral and constant for final answer...
[tex]\frac{1}{4}tan^4(x) - \frac{1}{2}tan^2(x) - ln|sec(x)| + C[/tex]

This was found to be incorrect. When I tried to use WolframAlpha to find the derivative to check if it could be an alternate answer, Wolfram couldn't deal with it and instead gave me the natural log of secant. 0_0

Any help would be greatly appreciated.
 
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  • #2
Nothing wrong with your work. I think you're just forgetting that the integral of tan(x) can be represented as ln|secx| or -log(cos(x)). Try it with cosx and you'll get the same answer as Wolfram.


F
 
  • #3
Ah, thanks! I had a hunch.
 

1. What is the general formula for integrating tan^5(x)?

The general formula for integrating tan^5(x) is ∫ tan^5(x) dx = (1/6) tan^6(x) - (1/4) tan^4(x) + (1/2) tan^2(x) + C, where C is the constant of integration.

2. How is the integral of tan^5(x) different from the integral of tan(x)?

The integral of tan^5(x) is different from the integral of tan(x) because the power of the tangent function is higher in the former. This means that the integration process is more complex and involves more steps.

3. Can the integral of tan^5(x) be solved using substitution?

Yes, the integral of tan^5(x) can be solved using substitution. One possible substitution is u = tan(x), which can simplify the integral to the form of ∫ u^4 du. However, other substitution methods can also be used.

4. What are some applications of integrating tan^5(x)?

Integrating tan^5(x) can be useful in solving problems related to mechanics, such as calculating the work done by a variable force or the displacement of an object under the influence of varying acceleration. It can also be applied in calculating the area under certain curves in mathematics and physics.

5. Are there any common mistakes to avoid when integrating tan^5(x)?

One common mistake to avoid when integrating tan^5(x) is forgetting to add the constant of integration. Additionally, it is important to carefully handle the different powers of tangent and make sure all terms are correctly included in the final solution. It is also helpful to double check the solution using differentiation.

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