Let $f(x)=x^3-6 x^2+9 x+18$, then f(x) is strictly decreasing in
Answer & explanation
Correct answer: option 4
$f(x) =x^3-6 x^2+9 x+18$
$f'(x) =3 x^2-12 x+9$
$=3\left(x^2-4 x+3\right)$
$=3(x-1)(x-3) \leq 0$
$x \in[1,3]$
Let $f(x)=x^3-6 x^2+9 x+18$, then f(x) is strictly decreasing in
Correct answer: option 4
$f(x) =x^3-6 x^2+9 x+18$
$f'(x) =3 x^2-12 x+9$
$=3\left(x^2-4 x+3\right)$
$=3(x-1)(x-3) \leq 0$
$x \in[1,3]$