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\(\int \frac{\sin 4\theta}{\sin 2\theta}d\theta =\)

  • A.\(\frac{\sin\theta}{2} + C\)
  • B.\(\cos 2\theta + C\)
  • C.\(2\sin 2\theta + C\)
  • D.\(\frac{\cos\theta}{2} + C\)
  • E.\(\sin 2\theta + C\)

Answer: E

The integral is \(\sin 2\theta + C\).

Since \(\sin 4\theta = 2\sin 2\theta\cos 2\theta\), the integrand is \(2\cos 2\theta\):

\[ \int 2\cos 2\theta\,d\theta = \sin 2\theta + C \]

\(2\sin 2\theta\) forgets to divide by the 2 from the chain rule, \(\cos 2\theta\) is a derivative of the wrong kind, and the options in \(\sin\theta\) or \(\cos\theta\) do not differentiate back to \(2\cos 2\theta\).

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