Write the Word or Phrase That Best Completes Each Statement $$\cos \left( x + \frac { \pi } { 6 } \right) = \frac { \sqrt { 3 } } { 2 } \cos x - \frac { 1 } { 2 } \sin x$$

Essay

Write the word or phrase that best completes each statement or answers the question.
Establish the identity.
- $$\cos \left( x + \frac { \pi } { 6 } \right) = \frac { \sqrt { 3 } } { 2 } \cos x - \frac { 1 } { 2 } \sin x$$