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JEE Advanced
Exam
JEE Advanced
Subject
Mathematics
Chapter
Trigonometry

JEE Advanced · Mathematics · Trigonometry

If 4+ 8- 32+ 768 =a 2 ((11 π)/(b)), where a and b are natural...

If 4+8−32+768=a2cos⁡(11πb),where\sqrt{4+\sqrt{8-\sqrt{32+\sqrt{768}}}}=a \sqrt{2} \cos \left(\frac{11 \pi}{b}\right), wherea and bb are natural numbers then \frac{b}{a} is divisible by

Options

  1. A2
  2. B4
  3. C3
  4. D6

Correct answer

D. 6

Step-by-step solution

 Let 768=32cos⁡θ163=32cos⁡θcos⁡θ=32⇒θ=π6\begin{aligned} & \text { Let } \sqrt{768}=32 \cos \theta \\ & 16 \sqrt{3}=32 \cos \theta \\ & \cos \theta=\frac{\sqrt{3}}{2} \Rightarrow \theta=\frac{\pi}{6} \end{aligned}\text { So } \sqrt{4+\sqrt{8-\sqrt{32+32 \cos \frac{\pi}{6}}}}=\sqrt{4+\sqrt{8-8 \cos \frac{\pi}{12}}}=\sqrt{4+4 \sin \frac{\pi}{24}}=\sqrt{4+4 \cos \frac{11 \pi}{24}}=\sqrt{4\left(1+\cos \frac{11 \pi}{24}\right)}=\sqrt{4.2 \cos ^2 \frac{11 \pi}{48}}=2 \sqrt{2} \cos \frac{11 \pi}{48}SoSo\mathrm{a}=2, \mathrm{~b}=48\therefore \frac{\mathrm{b}}{\mathrm{a}}=24$
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