Is y a function of x? Why?

Question

y = -4x² - 8x - 7

Answer 1

The graph is a parabola opening downward. The graph passes the Vertical Line Test (every vertical line intersects the graph once and only once). Each x-value corresponds to one and only one y-value. So, y is a function of x.

Answer 2

f(x) = -4x² -8x -7 and y = -4x² -8x -7 mean exactly the same thing.

g(w) = -4w² -8w -7 also means exactly the same thing.