Sketching a Quadratic Graph
To sketch a graph we need to find a set of points. This is most easily done by drawing up a table. The table for the graph given by the equation
| -3 | -2 | -1 | 0 | 1 | 2 | 3 |
| 9 | 4 | 1 | 0 | 1 | 4 | 9 |
| 3 | 2 | 1 | 0 | -1 | -2 | -3 |
| 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 13 | 7 | 3 | 1 | 1 | 3 | 7 |
When filling in the table the most important thing to remember is that when you square a minus number you obtain a positive number, eg
not -9.
DO NOT RELY ON YOUR CALCULATOR TO WORK OUT THE SQUARE OF A MINUS NUMBER.
Your calculator will tell you that
which is exactly wrong:
is correct. The graph is shown below.
