Question

If \( \cos\theta=\frac{1}{2}\left(a+\frac{1}{a}\right) \), then \(4\cos^3\theta-3\cos\theta=\)

• A. \(a^3+\frac{1}{a^3}\)
• B. \(\frac{1}{2}\left(a^3+\frac{1}{a^3}\right)\)
• C. \(\frac{1}{4}\left(a^3+\frac{1}{a^3}\right)\)
• D. \(\frac{1}{3}\left(a^3+\frac{1}{a^3}\right)\)

Hint:

Whenever you see \(4\cos^3\theta-3\cos\theta\), immediately remember it is equal to \(\cos 3\theta\).

Answer 1

The Correct Option is B