#:.int1/(e^x+1)dx=x -ln (e^x+1) +c#
Where #c# is the constant of integration
Explanation:
#int1/(e^x+1)dx=int (1-e^x/(e^x+1))dx# #=x-inte^x/(e^x+1)dx#
Now for #inte^x/(e^x+1)dx # substitute #e^x=t# then #e^xdx=dt#
Hence the integral becomes #intdt/(t+1)=ln (t+1)+c# #:.inte^x/(e^x+1)dx= ln (e^x+1)+c# #:.int1/(e^x+1)dx=x -ln (e^x+1)+c#