# Indefinite integral substitution

1. Oct 20, 2006

### sapiental

evaluate the indefinite integral ((e^x)/((e^x)+1))dx

I let u = ((e^x)+1)

then

du = (e^x)dx

which occurs in the original equation so..

indefinite ingegral ((u^-1)du)

taking the antiderivative I get 1 + C

is this right? thanks!!

2. Oct 20, 2006

### courtrigrad

$$\int \frac{e^{x}}{e^{x}+1} dx$$

it should be $$\ln|e^{x}+1| + C$$ because it is of the form $$\int \frac{du}{u}$$

Last edited: Oct 20, 2006
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