Integration, u substitution with limits

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SUMMARY

The discussion focuses on solving the integral ∫x/√(x+1) dx with limits from 0 to 1 using the substitution x = u² - 1. The substitution leads to new limits of √2 and 1 for u. The integral simplifies to ∫(u - 1/u) du, resulting in the expression 1/2(u)² - ln(u). The final evaluation of the integral at the new limits reveals a common mistake in handling the limits and substitution steps, which was clarified by another participant.

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sg001
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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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hi sg001! :smile:
sg001 said:
dx = du

noooo :redface:
 
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.
 

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