Bonjour,
f'(x) = 9x² - 4
on pose f'(x) = 0 → 9x² - 4 = 0 → (3x)² - 2² = 0 (3x + 2)(3x - 2) = 0 donc x = -2/3 ou x = 2/3
x...........|-∞............-⅔................⅔............+∞
f'(x).......|.........+......0.........-.........0.....+........
f(x).......|..........↑.................↓................↑........