First observe that the left hand side evaluates to 0 whenever

,

, or

.
So let's take numbers to either side of these roots. If

, for instance, we have

,

, and

. We would be multiplying a positive number (2) by two negatives (-1 and -8) and a positive (36), which gives a positive number. So, we know

must be a solution set.
Doing the same for numbers between/beyond the other three cases,

,

, and

, we would get, respectively, a negative, positive, and a positive.
The entire solution set would then be the union of the intervals over which we get a positive number, i.e.
