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\(\int \frac{x}{5 - x^{2}}dx =\)

  • A.\(\frac{-1}{2}\log_{e}\left|\frac{1}{5 - x^{2}}\right| + C\)
  • B.\(\frac{1}{2}\log_{e}|5 - x^{2}| + C\)
  • C.\(-2\log_{e}|5 - x^{2}| + C\)
  • D.\(\frac{-1}{2}\log_{e}|5 - x^{2}| + C\)
  • E.\(2\log_{e}\left|\frac{1}{5 - x^{2}}\right| + C\)

Answer: D

The integral is \(-\frac{1}{2}\log_{e}|5 - x^{2}| + C\).

The derivative of \(5 - x^{2}\) is \(-2x\), so write the numerator as \(-\frac{1}{2}(-2x)\):

\[ \begin{aligned} \int\frac{x}{5 - x^{2}}dx \\ &= -\frac{1}{2}\int\frac{-2x}{5 - x^{2}}dx \\ &= -\frac{1}{2}\log|5 - x^{2}| + C \end{aligned} \]

The option \(\frac{1}{2}\log|5 - x^{2}|\) has the wrong sign; note that \(-\frac{1}{2}\log\left|\frac{1}{5 - x^{2}}\right|\) equals that same wrong expression. The options with coefficient \(\pm 2\) do not differentiate back to the integrand.

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