Inflection points occur where
If at and , for example,
then your intervals are
You can determine the concavity of an interval by checking any value within that interval using
For the interval , you could use the number -10
If is positive, then that interval is concave up.
If is negative, then that interval is concave down.
Also, if is negative on both sides or positive on both sides, then there is no inflection point at x.
Can you figure it out from there?