$(1$ point$)$ Let $f(x)=-x^4-2x^{3}2x-6.$ Find the epen intervals on which $f$ is concave se $($isome$)$ Then detarmine the $x-$coordinates of all inflection peints of $f$

$f$ is concave up on the inferval $$

$f$ is concave down on the intervali $$

The inflection points occur at $x=$

Notes: In the first two, your answer should either be a single interval, such as $($p$,1),$ a comma smparated list of intervals, such as $(-$ief, $2),(3,4),$ or the word "none"

In the last one, your answer should be a comma separated list of $x$ values or fies wond "none".

Note: You can eam partial credit on this problem.