If $f(x)=\int \frac{d x}{\left(x^2+2\right)}$ and $f(\sqrt{2})=0$, then $f(0)=$

If $f(x)=\int \frac{d x}{\left(x^2+2\right)}$ and $f(\sqrt{2})=0$, then $f(0)=$
  1. $\frac{\pi}{2 \sqrt{2}}$
  2. $\frac{-\pi}{2 \sqrt{2}}$
  3. $\frac{-\pi}{4 \sqrt{2}}$
  4. $\frac{\pi}{4 \sqrt{2}}$

Solution

$\quad f(x)=\int \frac{d x}{x^2+(\sqrt{2})^2}=\frac{1}{\sqrt{2}} \tan ^{-1}\left(\frac{x}{\sqrt{2}}\right)+c$ Since at $x=\sqrt{2}, f(x)=0$ $ \Rightarrow 0=\frac{1}{\sqrt{2}} \tan ^{-1}(1)+c \Rightarrow c=-\frac{\pi}{4 \sqrt{2}} $ Hence $ f(0)=\frac{1}{\sqrt{2}} \tan ^{-1}\left(\frac{0}{\sqrt{2}}\right)+\left(-\frac{\pi}{4 \sqrt{2}}\right)=-\frac{\pi}{4 \sqrt{2}} $

Asked in: AP EAMCET 2023 (15 May Shift 1)

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