Blue graph (on the left): a is the horizontal axis, b is the vertical axis.

Green graph (on the right: x is the horizontal axis, y is the vertical axis.

y = -x^2 - b * x + a
y = -x^2 + 5 * x - 6 y = x^2 - 14 * x + 48
y = x^2 + 14 * x + 48 y = x^2 + x - 2
y = -x^2 + 11 * x - 28 y = -x^2 - 8 * x - 15