The function f(x)=2x3–3x2–12x+8 has maximum at x =
– 1
2
f′(x)=6x2–6x–12
f”(x) = 12x – 6
f’(x) = 0 ⇒ x2 – x – 2 = ⇒ x = – 1, 2
f’’(-1) 0 ⇒ f(x) has maxi. at x = – 1