Answer:
C. -1 < x < 2.
Step-by-step explanation:
Change to vertex form to find the axis of symmetry:
x^2 − x −1
= (x - 0.5)^2 - 0.25 - 1
= (x - 0.5)^2 - 1.25.
Thus the graph is symmetrical about x = 0.5.
So the interval must be equal lengths either side of x = 0.5.
That would be -1 < x < 2.
