Integration by parts

  • Thread starter Panphobia
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  • #1
435
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Homework Statement


∫x*cos(x^2) dx

I tried using integration by parts, but the integral of cos(x^2) is very long, and I couldn't get it completely with my knowledge at the moment, so is there an easier way to solve this problem?
 

Answers and Replies

  • #2
Dick
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Homework Helper
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Homework Statement


∫x*cos(x^2) dx

I tried using integration by parts, but the integral of cos(x^2) is very long, and I couldn't get it completely with my knowledge at the moment, so is there an easier way to solve this problem?
Yes, don't use integration by parts. Use u substitution. Put u=x^2.
 
  • #3
435
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So the definite integral [0, sqrt(pi)] would be 0 correct?
 
  • #4
34,526
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Yes, correct.
Also, when you're working with integrals, it's usually best to see if a simple substitution will work before tackling it with integration by parts. Integration by substitution is usually a simpler approach that integration by parts, so if it doesn't work out, you haven't wasted much time.

In this case, and as you saw, it's a very obvious substitution that works.

BTW, when you post a problem, you need to show what you have tried, even if it wasn't successful. That's a rule in this forum.
 

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