In which interval the function $f(x)=\frac{1}{3}x^3+\frac{1}{2}x^2-6x+8$ decreases?

$x < – 2$ $x > 2$ $– 3 < x < 2$ No where

$– 3 < x < 2$

$f ' x = x + x − 6 <0$ f(x) is a decreasing function if $f ' x <0$ $⇒x^2+x-6<0$ $⇒(x+3)(x-2)<0$ $– 3 < x < 2$