Find the interval of the monotonicity of the function f(x) = 2x3 – 12x2 + 18x + 5.
Given f(x) = 2x3 – 12x2 + 18x + 5
= 6x2 – 24x + 18
= 6(x2 – 4x + 3)
= 6(x – 1)(x – 3)
By the sign scheme, f(x) is strictly increases in (–∞, 1) ∪ (3, ∞) and strictly decreases in (1, 3)
