Write the Product as a Sum or Difference of Trigonometric $4 \cos 18 ^ { \circ } \cos 9 ^ { \circ }$

Write the product as a sum or difference of trigonometric functions.
- $4 \cos 18 ^ { \circ } \cos 9 ^ { \circ }$

A) $2 \left( \cos 27 ^ { \circ } - \cos 9 ^ { \circ } \right)$
B) $2 \left( \cos 27 ^ { \circ } + \cos 9 ^ { \circ } \right)$
C) $2 \left( \sin 27 ^ { \circ } - \sin 9 ^ { \circ } \right)$
D) $4 \left( \sin 27 ^ { \circ } + \sin 9 ^ { \circ } \right)$

Correct Answer:

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