# integration by substitutionWatch

#1
Hi im a little bit confused
when you use the substitution u=f(x) for an integration do u then multiply by du/dx or dx/du ?

thanks alot
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12 years ago
#2
The way I do it is:
u = f(x)
du/dx = f'(x)
dx/du = 1/f'(x)
dx = du/f(x)

Then just replace the dx in the integral with du/f'(x)
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12 years ago
#3
I find dx "in terms of " du and substitute in place of dx in the integral.
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12 years ago
#4
Replace "dx" by "dx/du * du" (easy to remember, the "du"s cancel).

Use dx/du = 1 / [du/dx].

Eliminate every x before you start to integrate wrt u.
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