AP EAMCET · Maths · Trigonometric Ratios & Identities
\(\cos ^3 110^{\circ}+\cos ^3 10^{\circ}+\cos ^3 130^{\circ}=\)
- A \(\frac{3}{4}\)
- B \(\frac{3}{8}\)
- C \(\frac{3 \sqrt{3}}{8}\)
- D \(\frac{3 \sqrt{3}}{4}\)
Answer & Solution
Correct Answer
(C) \(\frac{3 \sqrt{3}}{8}\)
Step-by-step Solution
Detailed explanation
\(\cos ^3 10+\cos ^3 110+\cos ^3 130^{\circ}\) We know that, \[ \cos ^3 x+\cos ^3(120-x)+\cos ^3(120+x)=\frac{3}{4} \cos 3 x \] Here, \[ x=10 \] Now, \(\cos ^3 10+\cos ^3 110^{\circ}+\cos ^3 130^{\circ}\)…
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