Mathematics for IGCSE & O level - Coordinate Geometry (Section 4 - No. 10)

Which of the following is not a form of a straight line equation?

y = mx + c

ax + by = c

y - y1 = m(x - x1)

y = ax^2 + bx + c

y = ax^2 + bx + c is the general form of a parabola (quadratic equation)