Solve

Question

(x+18)(x-18)(x+12)>0
Solution set is {x|-8,-12}
Is this correct?

Answer 1

The leading term of the cubic is positive, so for x->∞, the function f(x) approaches ∞.
There should in fact be two intervals where f(x) is >0, between the two smaller zeroes, and when x>the largest zero.
If you plot the function, it will make it clear.