Respuesta :

f(9.1) = 9.1(5-9.1) = -37.31
f(9) = 9 * -4 = -36

Approximate values of f'(9) =  [(-37.31) - (-36)] /   [9.1 - 9]   =  -1.31 / 0.1

=  -13.1  (answer)