Question:medium

The number of solutions of the equation \(1 + \sin x \cdot \sin^2 \frac{x}{2} = 0\) in \([-\pi, \pi]\) is

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Check the range of both sides of the equation.
Updated On: Jun 18, 2026
  • zero
  • 1
  • 2
  • 3
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The Correct Option is A

Solution and Explanation

To solve the given trigonometric equation \(1 + \sin x \cdot \sin^2 \frac{x}{2} = 0\) in the interval \([-\pi, \pi]\), we need to find the values of \(x\) that satisfy the equation. Let's break down the problem step-by-step:

  1. The equation is given as: \(1 + \sin x \cdot \sin^2 \frac{x}{2} = 0\)
  2. Rearrange the equation to isolate the trigonometric expression: \(\sin x \cdot \sin^2 \frac{x}{2} = -1\)
  3. Notice that: \(|\sin x| \leq 1\) and \(|\sin^2 \frac{x}{2}| \leq 1\)
  4. Therefore, \(|\sin x \cdot \sin^2 \frac{x}{2}| \leq 1\). Hence, \(\sin x \cdot \sin^2 \frac{x}{2}\) cannot be equal to \(-1\) based on the range of sine functions.

Since it is impossible for the product of two terms, each bounded within \([-1, 1]\), to equal \(-1\), the equation has no solutions.

Conclusion: The number of solutions of the equation in the interval \([-\pi, \pi]\) is zero.

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