Answer
Answers may vary.
$y=-x^2-x-1$ is one answer
Work Step by Step
The axis of symmetry also provides the maximum or minimum value for a function (if the value of $a$ is negative or positive, respectively).
Since the graph is entirely below the x-axis, we know the axis of symmetry will provide the maximum value.
$y=-x^2-x-1$
$x=-b/2a$
$x=-(-1)/2*(-1)$
$x = 1/-2$
$x=-1/2$
$y=-x^2-x-1$
$y=-(-1/2)^2-(-1/2)-1$
$y=-1/4+1/2-1$
$y=1/4-1$
$y=-3/4$
