#### Answer

$0$

#### Work Step by Step

Recall:
(1) An angle and its reference angle either have the same trigonometric function values or differ only in signs.
(2) In a unit circle, $\cos{\theta} = x$
$\frac{3\pi}{2}$ is a special angle whose terminal side is the negative y-axis.
Note that the negative y-axis intersects the unit circle at the point $(0, -1)$
Therefore,
$\cos{\frac{3\pi}{2}} = 0$