Question 78255
In order to graph {{{y=x^2-x-2}}} lets make a table:
<pre>

      x      y
   -5.0   28.0
   -4.0   18.0
   -3.0   10.0
   -2.0    4.0
   -1.0    0.0
    0.0   -2.0
    1.0   -2.0
    2.0    0.0
    3.0    4.0
    4.0   10.0
    5.0   18.0

</pre>

Now draw a parabola through these points

{{{ graph( 300, 200, -6, 5, -10, 10, x^2-x-2)}}}

In order to graph {{{y=2x^2-3x-9}}} lets make a table:
<pre>

     x      y
   -5.0   56.0
   -4.0   35.0
   -3.0   18.0
   -2.0    5.0
   -1.0   -4.0
    0.0   -9.0
    1.0  -10.0
    2.0   -7.0
    3.0    0.0
    4.0   11.0
    5.0   26.0

</pre>

Now draw a parabola through these points

{{{ graph( 300, 200, -6, 5, -10, 10, 2x^2-3x-9) }}}

So now use the quadratic formula for each case to find the x-intercepts

*[invoke quadratic "x", 1, -1, -2 ]


So the x-intercepts are (-1,0) and (2,0)


*[invoke quadratic "x", 2, -3, -9 ]


So the x-intercepts are (-1.5,0) and (3,0)