Penyelesaian:
f(x) = 2x³ – 9x² – 60x – 11
f՛(x) = 2 × 3x³⁻¹ – 9 × 2²⁻¹ – 60 × 1x⁻¹ – 0
= 6x² – 18x – 60
Fungsi f(x) mencapai stasioner bila f՛(x) = 0.
f՛(x) = 0
⇔ 6x² – 18x – 60 = 0
⇔ 6(x² – 3x – 10) = 0
⇔ 6(x + 2)(x – 5) = 0
⇔ x = -2 atau x = 5
Kaprikornus, grafik fungsi f(x) = 2x³ – 9x² – 60x – 11 naik pada interval x < -2 atau x > 5.