Verified answer

f(x) = -x³ +3x² +9x - 29

f'(x) = -3x² + 6x + 9

-3x² + 6x + 9 = 0 | : (-3)

x² - 2x - 3 = 0

по т. Виета:

x₁ = -1, x₂ = 3

f(-1) = - (-1)³ + 3 (-1)² + 9 (-1) - 29 = 1 + 3 - 9 - 29 = -34

f(3) = -2

f(4) = -9

Ответ: -2.