we have

we know that
the equation of a vertical parabola in vertex form is equal to

where
is the vertex
If
------> then the parabola open upward (vertex is a minimum)
If
------> then the parabola open downward (vertex is a maximum)
In this problem
the vertex is the point


so
------> then the parabola open downward (vertex is a maximum)
The domain is the interval-------> (-∞,∞)
that means------> all real numbers
The range is the interval--------> (-∞, -1]

that means
all real numbers less than or equal to

therefore
the answer is
a) the vertex is the point

b) the domain is all real numbers
c) the range is

see the attached figure to better understand the problem