grafik fungsi f(x)=x³-2x²+x+5 turun pada interval

Turun maka f'(x) < 0
f(x) = x³ - 2x² + x + 5 ⇒ f'(x) = 3x² - 4x + 1

Batas interval
f'(x) < 0
3x² - 4x + 1 < 0
3x² - x - 3x + 1 < 0
(3x² - x) - (3x - 1) < 0
x(3x - 1) - (3x - 1) < 0
(x - 1)(3x - 1) < 0
x = 1 atau x = 1/3

Turun pd interval 1/3 < x < 1.