Comprehension

Consider the following for the two (02) items that follow:

Let the function y = (1 - cos x)-1 where\(x \ne 2n\pi\) and n is an integer

What is ydx equal to? 

where c is the constant of integration.

This question was previously asked in
NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. tan(x/2)+c
  2. cot(x/2)+c
  3. tan(x/2)+c
  4. cot(x/2)+c

Answer (Detailed Solution Below)

Option 2 : cot(x/2)+c
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Detailed Solution

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Calculation:

Given,

The function is \(y = \left(1 - \cos(x)\right)^{-1} \), where\(x \neq 2n\pi \) and n is an integer.

The given function can be written as:

\( y = \frac{1}{1 - \cos(x)} \)

Using the identity \(1 - \cos(x) = 2\sin^2\left(\frac{x}{2}\right) \), we rewrite the function as:

\( y = \frac{1}{2\sin^2\left(\frac{x}{2}\right)} \)

The integral we need to evaluate is:

\( \int \frac{dx}{2\sin^2\left(\frac{x}{2}\right)} \)

\( \frac{1}{2} \int \csc^2\left(\frac{x}{2}\right) dx \)

The integral of \(\csc^2(x) \) is known to be \( -\cot(x) \), so we get:

\( \frac{1}{2} \left( -\cot\left(\frac{x}{2}\right) \right) + C \)

\( -\frac{1}{2} \cot\left(\frac{x}{2}\right) + C \)

The final result is \( -\cot\left(\frac{x}{2}\right) + C \)

Hence, the correct answer is Option 2.

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