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Let the set of all \(a \in R\) such that the equation \(\cos 2 x+a \sin x=2 a-7\) has a solution be \([p, q]\) and \(r=\tan 9^{\circ}-\tan 27^{\circ}-\frac{1}{\cot 63^{\circ}}+\tan 81^{\circ}\), then pqr is equal to _____.

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Best answer

Correct answer: 48

\(\cos 2 \mathrm{x}+\mathrm{a} \cdot \sin \mathrm{x}=2 \mathrm{a}-7\)

\(\mathrm{a(\sin x-2)=2(\sin x-2)(\sin x+2)}\)

\(\sin \mathrm{x}=2, \mathrm{a}=2(\sin \mathrm{x}+2)\)

\(\Rightarrow \mathrm{a} \in[2,6]\)

\(\mathrm{p=2 \quad q=6}\)

\(\mathrm{r=\tan 9^{\circ}+\cot 9^{\circ}-\tan 27^{\circ}-\cot 27}^{\circ}\)

\(\mathrm{r}=\frac{1}{\sin 9 \cdot \cos 9}-\frac{1}{\sin 27 \cdot \cos 27}\)

\(=2\left[\frac{4}{\sqrt{5}-1}-\frac{4}{\sqrt{5}+1}\right]\)

\(\mathrm{r}=4\)

\(\mathrm{p} \cdot \mathrm{q} \cdot \mathrm{r}=2 \times 6 \times 4=48\)

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