Efficient Integration of x^5 exp(x^2) in First-Year Calculus

  • Thread starter kingwinner
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In summary: For the integral of x^n exp(x^2) when n is even, you will need to use the substitution u=xn, du=2xnx.
  • #1
kingwinner
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Homework Statement


I am losing my first year calculus skills :(
I don't remember how to integrate x5 exp(x2).
What is the fastest way?


Homework Equations


N/A


The Attempt at a Solution


Maybe we need to integrate by parts? But how should I set u and dv?


Thanks for any help!
 
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  • #2
I would go with integration by parts. There are various possibilities for u and dv, but the one I would try first is u = x4, dv = xex2dx. A good strategy for integration by parts is to choose dv so that it is the most complicated thing that you can actually integrate.

The goal is to get an integral with x to a power less than 5, and keep applying integration by parts until you get a fairly simple integral, like [tex]\int xe^{x^2}dx[/tex], which can be done by an ordinary substitution.
 
  • #3
If you are familiar with the trick of tabular integration for integration by parts, you can use the substitution u=x², du=2xdx, to get the solution faster without having to perform multiple integrations by parts.
 
  • #4
How many times do I have to integrate by parts?
 
  • #5
Depending on the substitution used, at least 2 times.
 
  • #6
This integral actually occurs in the middle of a statistics problem. If I know the expectation of a gamma distribution, can I possibly avoid integrating by parts in the above integral? If so, how?
 
  • #7
kingwinner said:
This integral actually occurs in the middle of a statistics problem. If I know the expectation of a gamma distribution, can I possibly avoid integrating by parts in the above integral? If so, how?
I don't know anything about that. You posed the problem, and you have gotten a couple of strategies for solving it. If you don't know how to do integration by parts, say so, and we'll help you out.
 
  • #8
Another method that works here is to substitute u=x^2 ...
This will work for the integral of x^n exp(x^2) when n is odd.
 

Related to Efficient Integration of x^5 exp(x^2) in First-Year Calculus

What is the general formula for integrating x^5 exp(x^2)?

The general formula for integrating x^5 exp(x^2) is ∫x^n exp(ax)dx = (x^(n+1)/a)*exp(ax) - n/(a^2)*∫x^(n-1)exp(ax)dx, where n is a positive integer and a is a constant.

What is the technique for solving integrals of the form x^5 exp(x^2)?

The technique for solving integrals of the form x^5 exp(x^2) is to use integration by parts, where we choose u = x^5 and dv = exp(x^2)dx. This will allow us to reduce the power of x in u and simplify the integral.

Can we use any other methods to integrate x^5 exp(x^2)?

Yes, we can also use substitution to solve this integral. We can let u = x^2, du = 2x dx and rewrite the integral as ∫x^3 exp(u)du. This can then be solved using the power rule for integration.

What is the final answer after integrating x^5 exp(x^2)?

The final answer after integrating x^5 exp(x^2) is (x^6/2)*exp(x^2) - 15/4*∫x^3 exp(x^2)dx + C, where C is the constant of integration.

Is there a way to check if our answer for the integral of x^5 exp(x^2) is correct?

Yes, we can check our answer by taking the derivative of our solution. If the derivative matches the original integrand, then our solution is correct. In this case, the derivative of (x^6/2)*exp(x^2) - 15/4*∫x^3 exp(x^2)dx + C is indeed x^5 exp(x^2), so our solution is verified.

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