x is less than or equal to -4 or x is greater than or equal to 5
x <= -4 or x>= 5
There is no intersection of both inequalities when we graph it in number line So, we write the interval notation separately for each inequality
for x<=-4 , x starts at -4 and goes to -infinity because we have less than symbol. Also we have = sign so we use square brackets
Interval notation is (-∞ , -4]
for x>= 5 , x starts at 5 and goes to infinity because we have greater than symbol. Also we have = sign so we use square bracket at 5
Interval notation is [5 , ∞)
Now combine both notation by a 'U' symbol Union
(-∞ , -4] U [5 , ∞)