AP EAMCET · Maths · Trigonometric Ratios & Identities
\[
\left(4 \cos ^2 9^{\circ}-3\right)\left(4 \cos ^2 27^{\circ}-3\right)=
\]
- A \(\sin 9^{\circ}\)
- B \(\cos 9^{\circ}\)
- C \(\tan 9^{\circ}\)
- D \(\cot 9^{\circ}\)
Answer & Solution
Correct Answer
(C) \(\tan 9^{\circ}\)
Step-by-step Solution
Detailed explanation
\begin{aligned} &\left(4 \cos ^2 9^{\circ}-3\right)\left(4 \cos ^2 27^{\circ}-3\right) \\ &= \frac{1}{\cos 9^{\circ}}\left(4 \cos ^3 9^{\circ}-3 \cos 9^{\circ}\right) \times \frac{1}{\cos 27^{\circ}} \\ &\left(4 \cos ^3 27^{\circ}-3 \cos 27^{\circ}\right) \\ &= \frac{1}{\cos…
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