here, a=-1, b=-4,c=2
when we calculate,
we see that discriminant(D) is b²-4ac
as a<0, of it, is negative, the graph has a downward parabola.
D is positive, so the graph intersects the x axis at two points, whoch would be the roots and can be calculated by:
--------- ,(Root 1)
-------- (Root 2)
If a vertex is given(The point where the graph turns), then you can check by (-b/2a, -D/4a)