So, what is the problem asking for? Integration by Parts for ∫(z^3e^z)dz

In summary, integration by parts can be used to solve the integral ∫((z^3)(e^z ))dz by first setting u = z^3 and dv = e^z, and then continuing with the process using separate symbols for each step to avoid confusion and reduce errors.
  • #1
narutoish
25
0

Homework Statement


∫((z^3)(e^z ))dz

Homework Equations



I just tried u dv - ∫v du

The Attempt at a Solution



u = z^3 dv = e^z
du = 3z^2 v = e^z

= z^3e^z - ∫(3e^z (z^2)) dz

I got this far but after that if I try integration by parts again, it gets too confusing.
 
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  • #2
You just have to keep going. Parts, parts and parts again!
 
  • #3
narutoish said:

Homework Statement


∫((z^3)(e^z ))dz


Homework Equations



I just tried u dv - ∫v du


The Attempt at a Solution



u = z^3 dv = e^z
du = 3z^2 v = e^z

= z^3e^z - ∫(3e^z (z^2)) dz

I got this far but after that if I try integration by parts again, it gets too confusing.

Integrate [itex] ∫(3e^{z} (z^{2})) dz [/itex] with integration by parts till you get the term[itex] ∫e^{z}dz [/itex]
 
  • #4
narutoish said:

Homework Statement


∫((z^3)(e^z ))dz


Homework Equations



I just tried u dv - ∫v du


The Attempt at a Solution



u = z^3 dv = e^z
du = 3z^2 v = e^z

= z^3e^z - ∫(3e^z (z^2)) dz

I got this far but after that if I try integration by parts again, it gets too confusing.

You can avoid confusion by using some extra symbols. Let ##I = \int z^3 e^z \, dz##. Integration by parts gives you ##I = z^3 e^z - 3I_1##, where ##I_1 = \int z^2 e^z \, dz##. Now look at ##I_1## in the same way, etc. Using separate symbols like that helps to keep things straight and to reduce errors.
 

1. What is Integration by parts and when is it used?

Integration by parts is a technique used to evaluate integrals of the form ∫u dv. It is primarily used when the integral contains a product of two functions, and is not easily evaluated using other methods such as substitution or partial fractions.

2. How do you choose which function to assign as u and dv in Integration by parts?

The general rule is to choose u as the more complicated function, and dv as the simpler function. This is because the goal is to make the integral easier to evaluate, and often the derivative of the more complicated function will be simpler than the original function.

3. Can Integration by parts be used for definite integrals?

Yes, Integration by parts can be used for both indefinite and definite integrals. However, when using it for definite integrals, the integration by parts formula needs to be adjusted to account for the limits of integration.

4. Are there any special cases where Integration by parts is particularly useful?

Integration by parts is particularly useful when one of the functions in the integral is a polynomial and the other is an exponential, logarithmic, or trigonometric function. In these cases, the derivative of the polynomial will eventually become zero, simplifying the integration process.

5. Is there a specific order to follow when evaluating integrals using Integration by parts?

Yes, there is a specific order to follow when using Integration by parts. First, choose u and dv, then use the integration by parts formula to find the integral of the product of u and dv. This will result in a new integral, which can then be solved using the same process. Repeat until the integral is easily evaluated or until the derivative of u becomes zero.

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