Find the exact value of $$$2 \cos ^{3}\left(\frac{5}{18} \pi\right)-\frac{3}{2} \cos \left(\frac{5}{18} \pi\right)$$$. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... ....................................................................................................................................................

Mathematics

IGCSE&ALevel

CAIE

Exam No：9709_w21_qp_23 Year：2021 Question No：7(b)

Answer:

Use identity with $\theta=\frac{5}{18} \pi$
Obtain $\frac{1}{2} \cos \frac{5}{6} \pi$ and hence $-\frac{1}{4} \sqrt{3}$

Knowledge points:

2.3.1 understand the relationship of the secant, cosecant and cotangent functions to cosine, sine and tangent, and use properties and graphs of all six trigonometric functions for angles of any magnitude

Answer:

Knowledge points:

Solution:

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