Integration by Parts: Solving an Intricate Integral

In summary, the conversation suggests using u substitution as an easier method for solving the integral of x*cos(x^2)dx. It is advised to try simple substitutions first before resorting to more complex methods. The definite integral in this case would be 0 by using the substitution u=x^2. The importance of showing attempted solutions when seeking help is also mentioned.
  • #1
Panphobia
435
13

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?
 
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  • #2
Panphobia said:

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
So the definite integral [0, sqrt(pi)] would be 0 correct?
 
  • #4
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.
 

Related to Integration by Parts: Solving an Intricate Integral

1. What is integration by parts?

Integration by parts is a technique used in calculus to solve integrals involving products of functions. It is often used when the integral cannot be solved using basic integration techniques, such as substitution or u-substitution.

2. How does integration by parts work?

Integration by parts involves breaking down an integral into two parts, one of which is differentiated and the other is integrated. This allows for the integral to be rewritten in a different form, making it easier to solve.

3. When should integration by parts be used?

Integration by parts should be used when the integral involves a product of functions, and other basic integration techniques are not applicable. It is also useful when the integral involves a combination of polynomial, trigonometric, exponential, or logarithmic functions.

4. What is the formula for integration by parts?

The formula for integration by parts is: ∫ u dv = u*v - ∫ v du, where u is the function to be differentiated and dv is the function to be integrated. This formula can be remembered using the acronym "LIATE", which stands for logarithmic, inverse trigonometric, algebraic, trigonometric, and exponential functions.

5. Are there any tips for solving integrals using integration by parts?

Yes, there are a few tips that can make solving integrals using integration by parts easier. These include choosing u and dv strategically, using algebraic manipulation to simplify the integral before applying integration by parts, and using trigonometric identities to rewrite the integral in a more manageable form.

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