() is for <>
[] is for ≤≥
greater than 8 means
x>8 or
8 to infinity not counting 8 or
(8,∞)
less than or equal to -4 is
x≤-4 or
from -∞ to -4
or
(-∞,-4]
the infinity has a () sign since you cannot equal infinity, you can approach it
U is unity so
(-∞,-4] U (8,∞)
