Question 251466
There are a lot of absolute value signs, so we need to be careful. It appears, that your original expression can be simplified to

/(U)/^2 <= /2U/ <= 2/U/, where / U / means absolute value of U.

Checking some numbers will quickly get the desired answer.

U = 0 -> 0 <= 0 <= 0 [TRUE]

U = 1 -> 1 <= 2 <= 2 [TRUE]

U = 2 -> 4 <= 4 <= 4 [TRUE]

U = 3 -> 9 ~<= 6 <= 6 [FALSE]

The only values of U that will hold appear to be {-2, -1, 0, 1, 2}.

hope that helps.