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Provide Solution For R.D.Sharma Maths Class 12 Chapter 18  Indefinite Integrals Exercise  Revision Exercise Question 16 Maths Textbook Solution.

Answers (1)

Answer:

x-\log \left|e^{x}+1\right|+c

Given:

\int \frac{1}{e^{x}+1} d x

Hint:

Do integration by separation.

Solution:  

\int \frac{1}{e^{x}+1} d x

    =\int \frac{\left(e^{x}+1\right)\left(-e^{x}\right)}{e^{x}+1} d x

   =\int d x-\int \frac{e^{x}}{e^{x}+1} d x

  now, let e^{x}+1=u

  Differentiate it with respect to x

  \frac{d u}{d x}=e^{x}

 d u=e^{x} d x

  now,

 I=\int d x-\int \frac{1}{u} d u

  =x-\log |u|+c

  =x-\log \left|e^{x}+1\right|+c \quad\left(\because u=e^{x}+1\right)

 

 

 

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