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\(\int e^{x}\sec x(1 + tanx)\,dx\)

  • A.\(e^{x}sec^{2}x + C\)
  • B.\(e^{x}tanx + C\)
  • C.\(e^{x}\sec x + C\)
  • D.\(e^{x}tan^{2}x + C\)
  • E.\(e^{x}\sec x\ tanx + C\)

Answer: C

The integral is \(e^{x}\sec x + C\).

Expand the integrand as \(e^{x}(\sec x + \sec x\tan x)\). This has the form \(e^{x}\left(f(x) + f'(x)\right)\) with \(f(x) = \sec x\), since \(\frac{d}{dx}\sec x = \sec x\tan x\), and

\[ \int e^{x}\left(f(x) + f'(x)\right)dx = e^{x}f(x) + C \]

Check: \(\frac{d}{dx}(e^{x}\sec x) = e^{x}\sec x + e^{x}\sec x\tan x\). \(e^{x}\tan x\) would need \(\tan x + \sec^{2}x\) in the bracket, and \(e^{x}\sec x\tan x\) differentiates to something with \(\sec^{3}x\).

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