The minimum value of f(x) is at the solution of and if the solution is x = a, .
For f(x) = -1x^2 + 3.2x - 3.5, f'(x) = -0.2x + 3.2 and f''(x) = -0.2 which is negative for all values of x.
Solving f'(x) = 0 gives -0.2x + 3.2 = 0
=> x = 3.2/0.2 = 16
f(16) = 22.1