One of the best way to solve these kinds of questions is to draw 3-4 points and than conclude from that how graph will go.
Because this function is f(y) (x depends on y) you randomly take several y values and calculate x for them and those are your pairs of coordinates of several points.
y = 0 x = 0
y = 1 x = a
y = -1 x = a
y = 2 x = 4a
y = -2 x = 4a
So if you draw these points on graph you will see it opens in positive direction of x axis.
