求不定积分∫dx/(e^x+1)

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求不定积分∫dx/(e^x+1)

求不定积分∫dx/(e^x+1)
求不定积分∫dx/(e^x+1)

求不定积分∫dx/(e^x+1)
∫dx/(e^x+1)
=∫(1+e^x-e^x)dx/(e^x+1)
=∫dx-∫e^xdx/(e^x+1)
=x-∫d(e^x+1)/(e^x+1)
=x-ln(e^x+1)+C

令e^x=t,则x=lnt,dx=dt/t
∫dx/(e^x+1) =∫dt/(1+t)t=∫(1/t-1/(1+t))dt=∫dt/t-∫dt/(1+t)=lnt-ln(1+t)+C=ln(t/(t+1))+C=ln(e^x/(e^x+1))+C