Find the exact value of the expressions \cos(x+\beta), \sin(x+\beta) and \tan(x + \beta) under the following conditions:
$\sin(x) = \frac{4}{5}$, $x$ lies in quadrant I, and $\sin(\beta) = \frac{12}{13}$, $\beta$ lies in quadrant II.
a. $\cos(x + \beta) = $
(Simplify your answer. Type an exact answer, using radicals as needed. Use integers or fractions for any numbers in the expression.)