Question 126398
Brackets mean the number is included.  Parentheses mean it's not.  So [4,6) means 4<=x<6, where <= is "less than or equal to".  x can be 4, but not 6.  I hope that makes sense.

(1,2) means 1 < x < 2.  x is between 1 and 2, but cannot be 1 or 2.  On a number line, this looks like an open circle on 1 and an open circle on 3 with a line connecting them.  [2,3] means 2 <= x <= 3.  x is between 2 and 3, and can be 2 or 3.  On a number line, this looks like a closed dot on 2 and a closed dot on 3 with a line connecting them.  So if I wanted to say 2 < x < 5 I would say x is in the open interval (2,5).  If I wanted to say 4 <= x <= 8, you would say x is in the closed interval [4,8].  What I did at the beginning was use both at the same time.  If x is in the interval [4,6), then x is still between 4 and 6, but x can be 4 but not 6.  I hope that clarified it a little.