LetÕs begin this investigation by looking at several graphs of y = aX2, with varying values of a.  For this exploration we will look specifically at a=1,,5,-, and -5.  The graph of a=1 will be used as a control graph to compare with the graphs of the other values of a.  WeÕll start by looking at all of the graphs.






If we look specifically at the graphs of y= 5x2 and y=-5x2 as compared to y= x2 we can readily see the distinction between y= 5x2 and y=-5x2.  The graph of y=5x2 opens concave upwards while the graph of y=-5x2 opens concave downwards or we can simply say that y=-5x2 is y= 5x2 reflected over the x-axis.





We must also compare these graphs to the graph of y= x2.  Here we can see that the graphs of y= 5x2 and y=-5x2 are more narrow than the graph of y= x2.  This is a dilation, more specifically a vertical expansion of y= x2. 




Notice that the graph becomes steeper (more narrow) when a is increased to 5.  As a increases the graph continues to become steeper, hence the term vertical expansion.





Here we see the graph becomes wider for    0 < a <1.  This is called a vertical compression because the graph is wider and shorter.



Parabola Activity