Below is the graph of a quadratic function, showing where the function is increasing and decreasing. If we draw in the tangents to the curve, you will notice that if the gradient of the tangent is ...

If the speed is DECREASING, angle θ between the velocity and acceleration vectors is in the range of: 90° < θ ≤ 180°; that is, the tangential component points rearward of the motion. Shown below is an ...