In the Problem, T Is a Real Number and P $\left( - \frac { \sqrt { 39 } } { 8 } , \frac { 5 } { 8 } \right) \quad$

Multiple Choice

In the problem, t is a real number and P = (x, y) is the point on the unit circle that corresponds to t. Find the exact value of
the indicated trigonometric function of t.
- $\left( - \frac { \sqrt { 39 } } { 8 } , \frac { 5 } { 8 } \right) \quad$ Find $\cos t$

A) $- \frac { \sqrt { 39 } } { 5 }$
B) $\frac { 5 } { 8 }$
C) $- \frac { 8 \sqrt { 39 } } { 39 }$
D) $- \frac { \sqrt { 39 } } { 8 }$