Assuming∫ = the integral from (0-3)I am having trouble deciding what to sub in as u in this integration problem:

∫ x(sqrt(x+1)) dx

Thanks.

Printable View

- May 1st 2013, 01:50 PMWalshyEvaluating an Integral
Assuming

**∫ = the integral from (0-3)**I am having trouble deciding what to sub in as u in this integration problem:

**∫ x(sqrt(x+1)) dx**

Thanks. - May 1st 2013, 02:16 PMBradynsRe: Evaluating an Integral
Let $\displaystyle u = x+1$, $\displaystyle du = dx$

The integral can then be rewritten as:

$\displaystyle \int_{0}^{3} (u-1)(\sqrt{u})du$

I'm sure you can take it from here. :) - May 1st 2013, 02:17 PMPlatoRe: Evaluating an Integral
- May 1st 2013, 02:23 PMWalshyRe: Evaluating an Integral
Yes, I see. Thanks for the help guys.

- May 1st 2013, 02:31 PMPlatoRe: Evaluating an Integral
- May 2nd 2013, 07:49 PMBradynsRe: Evaluating an Integral
Given this, I should clarify that my bounds were regards to

**X**, so when you integrate, you should**back substitute U**so you are**in respect to X**before evaluation of the bounds.

You can change the bounds so that they are with respect to**U**and integrate.

Or, you can leave the bounds with regard to**X**, integrate with respect to**U**and then back substitute so that you end up with the original function (*f(x), not not f'(x)*) with respect to**X**.

__Same result.__