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An antiderivative of the tangent is

  • A.\( \tan^{2}x/2 + C \)
  • B.\( -\ln|\cos x| + C \)
  • C.\( \ln|\cos x| + C \)
  • D.\( \sec^{2}x + C \)

Answer: B

Write the tangent as a quotient and substitute \( u = \cos x \), with \( du = -\sin x\,dx \):

\[ \int \frac{\sin x}{\cos x}dx \;=\; -\int \frac{du}{u} \;=\; -\ln|u| + C \;=\; -\ln|\cos x| + C. \]

The same antiderivative is often written \( \ln|\sec x| + C \), the two differing only by the sign taken inside the logarithm

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