Notice that the function is a second-degree polynomial.
a) Since the leading coefficient is negative, the graph of f(x) corresponds to a parabola on the plane that opens downwards.
Therefore, the function has a maximum value.
b) To find the minimum of f(x), solve the equation f'(x)=0, as shown below
[tex]\begin{gathered} f^{\prime}(x)=0 \\ \Rightarrow-2(2x)-8=0 \\ \Rightarrow-4x-8=0 \\ \Rightarrow x=-2 \end{gathered}[/tex]
The minimum value of the function occurs at x=-2.
c) Then, the minimum value of the function is 1
[tex]f(-2)=-2(-2)^2-8(-2)-7=-8+16-7=1[/tex]