My teacher said to always use a parentheses when using the infinity symbol with interval notation. Could you explain why?

Question

Example: x ≥ -1
Interval notation would be [ -1, ∞ ) with a parentheses at the end instead of the square bracket. Please explain why. Thank you.

Answer 1

I hope this helps! :)

Use parentheses to represent infinity or negative infinity, since positive and negative infinity are not numbers in the usual sense of the word and, therefore, cannot be “equaled.” A few examples of an interval, or a set of numbers in which a solution falls, are [−2,6) , or all numbers between −2 and 6 , including −2.

you should imagine a number the tinniest bit greater than 5, and that is where the group of numbers begins. The parenthesis to the left of 5 is called a round bracket or an exclusive bracket.