Integrated and Frustrated

Level pending

Solve:

0 1 1 e x 1 + e x d x = ? \int_0^1 \frac{1-e^{-x}}{1+e^{-x}}dx=?


The answer is 0.24.

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1 solution

William Lockhart
Sep 23, 2020

Solution:

0 1 1 e x 1 + e x d x = 0 1 1 1 + e x d x 0 1 e x 1 + e x d x = 0 1 e x e x + 1 d x 0 1 e x 1 + e x d x \int_0^1 \frac{1-e^{-x}}{1+e^{-x}}dx=\int_0^1\frac{1}{1+e^{-x}}dx-\int_0^1\frac{e^{-x}}{1+e^{-x}}dx=\int_0^1\frac{e^x}{e^x+1}dx-\int_0^1\frac{e^{-x}}{1+e^{-x}}dx u = 1 + e x d u = e x d x u=1+e^x \to du=e^xdx v = 1 + e x d v = e x d x v=1+e^{-x} \to dv=-e^{-x}dx x = 0 x = 1 1 u d u + x = 0 x = 1 1 v d v = ln ( 1 + e x ) 0 1 + ln ( 1 + e x ) 0 1 = ln [ ( 1 + e x ) ( 1 + e x ) ] 0 1 = \int_{x=0}^{x=1} \frac{1}{u}du+\int_{x=0}^{x=1} \frac{1}{v}dv=\ln (1+e^x)|_0^1+\ln (1+e^{-x})|_0^1=\ln[(1+e^x)(1+e^{-x})]|_0^1= ln [ ( 1 + e 1 ) ( 1 + e 1 ) ] ln [ ( 1 + e 0 ) ( 1 + e 0 ) ] = ln [ ( 1 + e ) ( 1 + 1 e ) 4 ] 0.24 \ln [(1+e^1)(1+e^{-1})]-\ln [(1+e^0)(1+e^{-0})]=\ln\left[\frac{(1+e)(1+\frac{1}{e})}{4}\right] \approx \boxed{0.24}

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