Integration, u substitution with limits

In summary, the conversation discusses how to find the integral ∫x/√(x+1).dx with limits 1 & 0 using substitution x = u^2 -1. The summary provides the step-by-step process of solving the problem and identifies where the person stumbled and how they were able to correct their mistake.
  • #1
sg001
134
0

Homework Statement



find ∫x/√(x+1).dx with limits 1 & 0

using substitution x = u^2 -1


Homework Equations





The Attempt at a Solution



dx = du

x = u^2 -1

u = √( x+1)

sub limits of 1 & 0 into u.
Hence new limits of √2 & 1

Therefore,

∫ u^2 -1/ u

= ∫ u - 1/u
= 1/2 (u)^2 - ln u

Plugging in limits of √2& 1

(1/2 * 2 - ln √ 2 ) - (1/2)

= ( 1/2 - 1/2 ln (2))

Cant work out where I have stumbled, any ideas?
 
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  • #2
hi sg001! :smile:
sg001 said:
dx = du

noooo :redface:
 
  • #3
ohh that makes sense now because i had the same question but with different sub involved. ie u= x + 1,,, so I kinda got ahead of myself and skipped that step.
Thanks for pointing that out, I probabaly would never have realized.
 

FAQ: Integration, u substitution with limits

What is the purpose of u substitution in integration?

U substitution is a technique used to simplify the process of integration by substituting a complex expression with a new variable. This helps to transform the integrand into a more manageable form, making it easier to solve.

How do you perform u substitution with limits?

To perform u substitution with limits, you first need to substitute the variable in the limits as well. Then, integrate the new expression with respect to the substituted variable. Finally, substitute back the original variable in the limits to get the final answer.

Is u substitution always necessary in integration?

No, u substitution is not always necessary in integration. It is a useful technique for solving integrals involving complicated expressions or functions, but it may not always be the most efficient method.

Can u substitution be used for definite integrals?

Yes, u substitution can be used for definite integrals. However, the substitution must also be made in the limits of integration and taken into account when evaluating the integral.

Are there any limitations to using u substitution in integration?

One limitation of u substitution is that it may not always work for all integrals. There are certain integrals that cannot be solved using this technique, and other methods such as integration by parts may be necessary.

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