Respuesta :
I'm doing interval notations right now in pre-calculus, this how this notation should be written, (-∞,-2] or [4,∞), but this, (x ≤ -2] or [4 ≤ x), means the same thing. closed circle gets a bracket and an open circle gets a parenthesis, infinity always gets a parentheses because it is not a number. hope this helps