Use the Formula for the Cosine of the Difference of Two

Multiple Choice

Use the Formula for the Cosine of the Difference of Two Angles
- $\cos \left( \frac { 5 \pi } { 18 } - \frac { \pi } { 9 } \right)$

A) $\frac { \sqrt { 3 } } { 2 }$
B) $\frac { 1 } { 2 }$
C) $\frac { 1 } { 4 }$
D) 1 Identify α and β in the following expression which is the right side of the formula for cos (α - β) .