can anyone help me to find my mistake, I can't figure out what's wrong, probably something small.
the correct answer should be -5<=x<=4
I got -1<=x<=4
It's not so much a matter of a single "mistake" as that your whole concept is wrong! Do you understand that if x< y it does not necessarily follow that ? -3< 2 but 9 is NOT less than 4.
I would do this instead: solve the equation . Those points separate "<" and ">". Check one point in each interval to see if the the inequality is satisfied in that interval.