AP EAMCET · Maths · Trigonometric Ratios & Identities
\(\cos 20^{\circ}+\cos 30^{\circ}+\cos 40^{\circ}=\)
- A \(1-2 \sin 10^{\circ} \sin 15^{\circ} \sin 20^{\circ}\)
- B \(4 \cos 20^{\circ} \cos 30^{\circ} \cos 40^{\circ}\)
- C \(4 \cos 10^{\circ} \cos 15^{\circ} \cos 20^{\circ}\)
- D \(4 \cos 25^{\circ} \cos 30^{\circ} \cos 35^{\circ}\)
Answer & Solution
Correct Answer
(D) \(4 \cos 25^{\circ} \cos 30^{\circ} \cos 35^{\circ}\)
Step-by-step Solution
Detailed explanation
\(\cos 20^{\circ}+\cos 30^{\circ}+\cos 40^{\circ} = (\cos 40^{\circ}+\cos 20^{\circ})+\cos 30^{\circ}\) \(= 2 \cos \frac{40^{\circ}+20^{\circ}}{2} \cos \frac{40^{\circ}-20^{\circ}}{2} + \cos 30^{\circ} = 2 \cos 30^{\circ} \cos 10^{\circ} + \cos 30^{\circ}\)…
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