Integration by Parts 5x ln(4x)dx

In summary, the problem asks to use integration by parts to evaluate the integral of 5x ln(4x)dx. The key equation to use is ∫udv = uv - ∫vdu. The attempted solution is to make u = ln(4x) and solve from there. However, the mistake was made by not accounting for the derivative of ln(4x) which is 1/x. Once this is corrected, the correct answer is obtained.
  • #1
sashab
12
0

Homework Statement



Use integration by parts to evaluate the integral.
∫5x ln(4x)dx


Homework Equations



∫udv = uv - ∫vdu

The Attempt at a Solution


So here's my solution:
tumblr_n1a0635Kjb1tsd2vco1_500.jpg


But the computer is telling me I'm wrong :( We haven't learned how to integrate lnx yet, so the only choice I have is to make u = ln(4x) (even our textbook does this). Any help would be really appreciated! Thanks :)
 
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  • #2
sashab said:

Homework Statement



Use integration by parts to evaluate the integral.
∫5x ln(4x)dx


Homework Equations



∫udv = uv - ∫vdu

The Attempt at a Solution


So here's my solution:
tumblr_n1a0635Kjb1tsd2vco1_500.jpg


But the computer is telling me I'm wrong :( We haven't learned how to integrate lnx yet, so the only choice I have is to make u = ln(4x) (even our textbook does this). Any help would be really appreciated! Thanks :)
What is the derivative of ln(4x) ?
 
  • #3
SammyS said:
What is the derivative of ln(4x) ?

Oh whoops! I can't believe I didn't notice such an obvious mistake. Thanks, I got the right answer now. :)
 
  • #4
By the chain rule, the derivative of ln(4x) is (1/4x) times the derivative of 4x so (1/4x)(4)= 1/x.

Even simpler: ln(4x)= ln(x)+ ln(4) so its derivative is 1/x.
 

Related to Integration by Parts 5x ln(4x)dx

1. What is Integration by Parts?

Integration by Parts is a method used to solve integrals that involve products of functions. It uses the formula ∫u dv = uv - ∫v du, where u and v are chosen functions and du and dv are their respective differentials.

2. How do you solve Integration by Parts?

To solve Integration by Parts, you need to follow these steps:

  • Choose u and dv in the integral ∫u dv based on the LIATE rule (Logarithmic, Inverse Trigonometric, Algebraic, Trigonometric, Exponential).
  • Calculate du and v by taking the derivative and antiderivative of u and dv, respectively.
  • Substitute u, du, v, and dv into the formula ∫u dv = uv - ∫v du.
  • Simplify the resulting integral and solve for the unknown variable.

3. What is the purpose of using Integration by Parts?

The purpose of using Integration by Parts is to solve integrals that cannot be solved by other integration techniques, such as substitution or u-substitution. It allows us to break down a complex integral into simpler parts and solve it using the formula ∫u dv = uv - ∫v du.

4. Can Integration by Parts be used for any type of integral?

No, Integration by Parts can only be used for integrals that involve products of functions. It is not applicable for integrals that involve quotients or nested functions.

5. How do you use Integration by Parts to solve 5x ln(4x)dx?

To use Integration by Parts to solve 5x ln(4x)dx, we need to choose u and dv based on the LIATE rule. In this case, we can choose u = ln(4x) and dv = 5x dx. Then, we calculate du = (1/x)dx and v = (5/2)x^2. Substituting these values into the formula ∫u dv = uv - ∫v du, we get the simplified integral 5/2 x^2 ln(4x) - 5/2 x^2 dx. Finally, we solve for x using basic integration techniques to get the final answer.

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