As x consistently increases 2 jumps at a time, y first decreases (from 0 to -2) and then increases from -2 to -1, and then from -1 to 0. Clearly there must be a minimum (and turning point) between x = 0 and x = 2 where, as x increases, y first decreases and then increases.
(0, -2) is not necesssarily the minimum of this function on x, but is in itself the turning point, or is closest to the actual turning point
