Medium MCQ +4 / -1 PYQ · JEE Mains 2024

If $2 \sin ^3 x+\sin 2 x \cos x+4 \sin x-4=0$ has exactly 3 solutions in the interval $\left[0, \frac{\mathrm{n} \pi}{2}\right], \mathrm{n} \in \mathrm{N}$, then the roots of the equation $x^2+\mathrm{n} x+(\mathrm{n}-3)=0$ belong to :

  1. A $(0, \infty)$
  2. B Z
  3. C $\left(-\frac{\sqrt{17}}{2}, \frac{\sqrt{17}}{2}\right)$
  4. D $(-\infty, 0)$ Correct answer

Solution

<p>$$\begin{aligned} & 2 \sin ^3 x+2 \sin x \cdot \cos ^2 x+4 \sin x-4=0 \\ & 2 \sin ^3 x+2 \sin x \cdot\left(1-\sin ^2 x\right)+4 \sin x-4=0 \\ & 6 \sin x-4=0 \\ & \sin x=\frac{2}{3} \\ & \mathbf{n}=5 \text { (in the given interval) } \\ & x^2+5 x+2=0 \\ & x=\frac{-5 \pm \sqrt{17}}{2} \\ & \text { Required interval }(-\infty, 0) \end{aligned}$$</p>

About this question

Subject: Mathematics · Chapter: Trigonometric Functions · Topic: Trigonometric Ratios and Identities

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