To determine if the given relation is a function using the vertical line test, we need to check if any vertical line drawn on the graph intersects the relation at more than one point.
Since the described relation is a semicircle, it would look like a half-circle (either the upper half or the lower half). For a semicircle, when we draw a vertical line, it will intersect the semicircle at most once (if it intersects at all), since there is no section of the graph where it dips back down.
In this case, because the graph of a semicircle only intersects any vertical line once (for the upper half) or does not intersect at all (for the lower half), we conclude that:
Yes, the given relation is a function.