You can
put this solution on YOUR website!The x-coordinate of the vertex of a parabola in the form

is given by

.
The y-coordinate is then

.
The line of symmetry passes through the vertex, so the equation is

.
The maximum or minimum is the value of the function at

. Whether it is a maximum or minimum depends on whether the parabola opens up or down. If it is concave up (makes a valley rather than a hill), the point is a minimum, otherwise it is a maximum. You can tell which way the parabola opens by the sign on the lead coefficient. if

, it is concave down, if

, it is concave up, and, of course, if

you don't have a parabola at all.
Let's look at your specific problem:
First thing to note is that

, so this is a concave down parabola and the vertex is a maximum.

, so the x-coordinate of the vertex is

and the equation of the line of symmetry is

.
The value of the function at

, denoted

for your problem is

(not

!).
So the y-coordinate of the vertex and the maximum value of f is