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MHT CET · Maths · Indefinite Integration

\(\int \frac{\log \left(x^2+\mathrm{a}^2\right)}{x^2} \mathrm{~d} x=\)

  1. A \(\frac{-\log \left(x^2+\mathrm{a}^2\right)}{x}+\frac{1}{\mathrm{a}} \tan ^{-1} \frac{x}{\mathrm{a}}+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  2. B \(\frac{-\log \left(x^2+\mathrm{a}^2\right)}{x}+\frac{2}{\mathrm{a}} \tan ^{-1} \frac{x}{\mathrm{a}}+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  3. C \(\frac{\log \left(x^2+\mathrm{a}^2\right)}{x^2}-\frac{1}{\mathrm{a}} \tan ^{-1} \frac{x}{\mathrm{a}}+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  4. D \(\frac{\log \left(x^2+\mathrm{a}^2\right)}{x^2}-\frac{2}{\mathrm{a}} \tan ^{-1} \frac{x}{\mathrm{a}}+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
Verified Solution

Answer & Solution

Correct Answer

(B) \(\frac{-\log \left(x^2+\mathrm{a}^2\right)}{x}+\frac{2}{\mathrm{a}} \tan ^{-1} \frac{x}{\mathrm{a}}+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.

Step-by-step Solution

Detailed explanation

Let
\(\mathrm{I} =\int \frac{\log \left(x^2+\mathrm{a}^2\right)}{x^2} \mathrm{~d} x \)
\( =\int \log \left(x^2+\mathrm{a}^2\right) \cdot x^{-2} \mathrm{~d} x \)
\( =\log \left(x^2+\mathrm{a}^2\right) \int x^{-2} \mathrm{~d} x \) \(-\int\left\{\frac{\mathrm{d}}{\mathrm{d} x}\left[\log \left(x^2+\mathrm{a}^2\right)\right] \int x^{-2} \mathrm{~d} x\right\} \mathrm{d} x \)
\( =\log \left(x^2+\mathrm{a}^2\right) \cdot\left(-\frac{1}{x}\right)-\int \frac{2 x}{x^2+\mathrm{a}^2} \cdot\left(-\frac{1}{x}\right) \mathrm{d} x \)
\( =-\frac{\log \left(x^2+\mathrm{a}^2\right)}{x}+2 \int \frac{1}{x^2+\mathrm{a}^2} \mathrm{~d} x \)
\( =-\frac{\log \left(x^2+\mathrm{a}^2\right)}{x}+\frac{2}{\mathrm{a}} \tan ^{-1}\left(\frac{x}{\mathrm{a}}\right)+\mathrm{c}\)