Evaluate : \(\int\frac{1+x}{x+e^{-x}}\,dx\)
Q.2 (A) (iii) Evaluate : \(\int\frac{1+x}{x+e^{-x}}\,dx\)
Q.2 (A) (iii) Evaluate : \(\int\frac{1+x}{x+e^{-x}}\,dx\)
Best answer
Answer: \(\log\left|xe^x+1\right|+c\)
Multiply numerator and denominator by \(e^x\):
\(I=\int\frac{e^x(1+x)}{xe^x+1}\,dx\)
Put \(xe^x+1=t\). Then \((xe^x+e^x)\,dx=dt\), i.e. \(e^x(1+x)\,dx=dt\).
\(I=\int\frac{dt}{t}=\log|t|+c=\log\left|xe^x+1\right|+c\).
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