Ta có: \(f'\left( x \right) = 3{x^2} - 6x\)
a. \(f'\left( x \right) > 0 \Leftrightarrow 3{x^2} - 6x > 0 \Leftrightarrow x < 0\,\text{ hoặc }\,x > 2\)
b. \(f'\left( x \right) \le 3 \Leftrightarrow 3{x^2} - 6x \le 3 \)
\(\Leftrightarrow {x^2} - 2x - 1 \le 0 \Leftrightarrow 1 - \sqrt 2 \le x \le 1 + \sqrt 2 \)
