Question:

\[ \int \frac{dx}{\cos x \, (1 + \cos x)} = \; ? \] 

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$1 + \cos x = 2\cos^2(x/2)$.
Updated On: Apr 30, 2026
  • \(( \log(\sec x + \tan x) + 2\tan ( \frac{x}{2} ) + c ) \)
     

  • \(( \log(\sec x + \tan x) - 2\tan ( \frac{x}{2} ) + c ) \)
     

  • \(( \log(\sec x + \tan x) + \tan ( \frac{x}{2} ) + c ) \)

  • \(( \log(\sec x + \tan x) - \tan ( \frac{x}{2} ) + c )\)

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The Correct Option is D

Solution and Explanation

Step 1: Partial Fractions 

\[ \frac{1}{\cos x(1 + \cos x)} = \frac{(1 + \cos x) - \cos x}{\cos x(1 + \cos x)} = \frac{1}{\cos x} - \frac{1}{1 + \cos x} \]

Step 2: Simplify Terms

\[ = \sec x - \frac{1}{2\cos^2(x/2)} = \sec x - \frac{1}{2}\sec^2(x/2) \]

Step 3: Integrate

\[ \int \sec x\,dx - \frac{1}{2}\int \sec^2(x/2)\,dx \]

\[ = \log(\sec x + \tan x) - \frac{1}{2} \cdot \frac{\tan(x/2)}{1/2} + C \]

\[ = \log(\sec x + \tan x) - \tan(x/2) + C \]

Final Answer: (D)

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