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 :
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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