Practicing Success
The value of $\int\limits_0^{\infty} \frac{\log x}{1+x^2} d x$, is |
$\frac{\pi}{4}$ $\frac{\pi}{2}$ 0 none of these |
0 |
Let $I=\int\limits_0^{\infty} \frac{\log x}{1+x^2} d x$ Putting $x=\tan \theta$, we get $I=\int\limits_0^{\pi / 2} \log \tan \theta d \theta$ ...(1) $I=\int\limits_0^{\pi / 2} \log \tan(\frac{\pi}{2}-θ)dθ=\int\limits_0^{\pi / 2}\log \cot θdθ$ ...(2) Eq. (1) + Eq. (2) $2I=\int\limits_0^{\pi / 2}\log \tan θ\cot θdθ=\int\limits_0^{\pi / 2}0dθ=0$ $I=0$ |