multiplying a by 2 is stretching the graph vertically by a factor of two. essentially this pulls the graph upward, making the graph narrower. Imagine pulling on a rubber band. As you stretch it upwards, it gets taller, but it also gets narrower. This is also true of the parabola. You also know the parabola opens upwards because the equation is positive, and all positive parabola equations open upwards.
