Answer
$\frac{5}{8}$
Work Step by Step
$sin^{2}t$ + $cos^{2}t$ = 1
sin t = $\frac{\sqrt {39}}{8}$
$(\frac{\sqrt {39}}{8})^{2}$ + $cos^{2}t$ = 1
$\frac{39}{64}$ + $cos^{2}t$ = 1
$cos^{2}t$ = 1 -$\frac{39}{64}$
$cos^{2}t$ = $\frac{25}{64}$
cos t = $\sqrt \frac{25}{64}$ = $\frac{5}{8}$
