Why is the integration constant excluded when finding v in integration by parts?

In summary, when integrating \int udv=uv-\int vdu, if dv=e^x dx, the integration constant is not included in the calculation of v. However, when expanding the integral, it is important to consider the integration constant in the final result.
  • #1
Fizex
201
0
We know the formula is [tex]\inline{\int udv=uv-\int vdu}[/tex] but when you say that for example, [tex]dv=e^x dx[/tex], then why when you integrate to get v, you don't include the integration constant?

For this integral:
[tex]\int xe^{x}dx[/tex]
[tex]dv = e^x dx[/tex]
[tex]v = e^x + C[/tex]?
 
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  • #2
You can, in this case you would get
[tex]\int x e^x \, \mathrm dx = (e^x + C) x + \int (e^x + C) \, \mathrm dx = x (e^x + C) - (e^x + C x + C')[/tex]
If you expand
[tex]x e^x + C x - (e^x - C x + C') = (x - 1) e^x - C'[/tex]
 
  • #3
oh, haha, I was only paying attention to one side of the equation. Thanks.
 

Related to Why is the integration constant excluded when finding v in integration by parts?

1. What is integration by parts?

Integration by parts is a method used to solve integrals that involve the product of two functions. It is based on the product rule of differentiation and involves rewriting the integral in a form that allows for easier integration.

2. When should integration by parts be used?

Integration by parts should be used when the integral involves a product of functions where one function is difficult to integrate and the other function is easy to differentiate. This method can also be used when the integral involves a function multiplied by a variable raised to a power.

3. What is the formula for integration by parts?

The formula for integration by parts is ∫u dv = uv - ∫v du, where u and v are functions of x and dv and du are their respective derivatives. This formula is based on the product rule of differentiation.

4. How do you choose which function to assign as u and which as dv?

When using integration by parts, the function u should be chosen as the one that will become simpler when differentiated, and the function dv should be chosen as the one that can be easily integrated. A common method for choosing u is the acronym LIATE, which stands for Logarithmic, Inverse trigonometric, Algebraic, Trigonometric, and Exponential. The function that falls first in this list should be chosen as u.

5. Can integration by parts be used to solve definite integrals?

Yes, integration by parts can be used to solve definite integrals. After applying the formula and simplifying, the resulting integral can be evaluated at the limits to find the definite integral.

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