Question

What are the extrema of `f(x)=f(x)= -x^2+8x+7`?

Answer 1

it has local maximum at (4;23)

Explanation:

At the turning point f'(x) = 0. Thus -2x +8 = 0.
So x= 4 and y = f(4) at extremum (4;23). The shape of the graph (an upside down "cup" indicates that this is a maximum point)