linear inequalities.
posted by claire on .
i'm having a lot of trouble figuring out when to use a closed or an open interval.
do i use infinity in every question where both numbers are not defined?
insight?
thanks/

If no lower or upper or lower limit of an interval is specified, assume it is infinity (+ or )

Use an open when the sign is NOT including the anwser. Use a closed when the sign DOES include the answer.
Infinity is used when you have PARAELL lines. 
how can i tell if something is included or not?
the answers i'm getting are like:
z>3
which is the correct answer. but when i go to graph it in the computer, i always click the wrong representation of interval notation. 
The red arrow shows that all the values on the number line less than –3 are in the solution. The open circle at –3 shows us that –3 is not in the solution.
Like this? Why is 3 not in the solution? How can I tell?