Question:medium

If \(n \in \mathbb{N}\), then \(|\sin nx|\)

Show Hint

\(|\sin nx| \leq n|\sin x|\) by induction using \(|\sin(a + b)| \leq |\sin a| + |\sin b|\).
Updated On: Jun 16, 2026
  • \(\leq n|\sin x|\)
  • \(\geq n|\sin x|\)
  • \(= n|\sin x|\)
  • None of these
Show Solution

The Correct Option is D

Solution and Explanation

To solve this problem, we need to analyze the behavior of the expression \(|\sin nx|\) where \( n \in \mathbb{N} \). Here's a step-by-step analysis:

  1. We are considering the function \(|\sin nx|\). This is the absolute value of the sine of a multiple of \(x\).
  2. The maximum value of the sine function, \(\sin nx\), for any \(x\) is 1 and the minimum value is -1, thus \(|\sin nx|\) will range between 0 and 1 (i.e., \(0 \leq |\sin nx| \leq 1\)).
  3. Now, let's consider \(|\sin x|\). Similar to above, we have \(0 \leq |\sin x| \leq 1\). 
  4. Based on these observations, we compare the options given:
  5. Option 1: \(\leq n|\sin x|\)
    • This suggests that \(|\sin nx|\) is always less than or equal to \(n|\sin x|\). However, \(|\sin nx|\) can be greater than \(n|\sin x|\) or simply not scale directly with \(nx\). This doesn't hold universally.
  6. Option 2: \(\geq n|\sin x|\)
    • This suggests that \(|\sin nx|\) is always greater than or equal to \(n|\sin x|\). For small values of \(x\), \(|\sin nx|\) can be less than \(n|\sin x|\). Hence, this is incorrect.
  7. Option 3: \(= n|\sin x|\)
    • This suggests that \(|\sin nx|\) is always equal to \(n|\sin x|\). However, this is not generally true because \(|\sin nx|\) depends on the sine wave oscillations, not just a linear scaling with \(n\).
  8. None of the options given accurately describe the relationship in all cases. Therefore, the correct answer is None of these.

In conclusion, the option "None of these" is correct because \(|\sin nx|\) does not simply scale with \(n\) times \(|\sin x|\), due to the periodic nature of the sine function and the behavior of its amplitude.

Was this answer helpful?
0