Answer
All are positive.
Work Step by Step
$-640^{\circ}+2\cdot360^{\circ}=80^{\circ}$
$80^{\circ}$ is coterminal with $-640^{\circ}$ and is in the first quadrant. In the first quadrant $x$, $y$, and $r$ are positive and therefore all of its trigonometric function values are positive.