# What does [x] means in mathematics ?

1. Mar 16, 2006

### momentum

what does [x] means in mathematics ?

i have found [x]= "the greatest integer <=x "

is this true ?

then, what will be the answer of of .....
[3],[1.5],[-1.5],[3.5]

[3]=3
[1.5]=1
[-1.5]=-1
[3.5]=3

are these correct ?

2. Mar 16, 2006

### shmoe

[] meaning greatest integer is a common use of the [], but it can vary.You should check whatever book your problems are from, they should define what they mean by the notation.

If it is the greatest integer function, then "[-1.5]=-1" isn't correct. You want the greatest integer less than or equal to -1.5, so it can't be -1 as -1.5<-1.

3. Mar 16, 2006

### Staff: Mentor

So, in what way is the defintion for $$[ x ]$$ you've given different from $$\lfloor x \rfloor$$ ? - also given to be the symbol for the floor function, which matches the definition you gave.

None, AFAIK, just a "who's the author" thing.

IMO, it's just a bad nomen confusum problem. I've also seen it used in characteristic functions. Somebody ought to pick one use, and pitch the rest.... :) and penalize deviating authors 10 points for misuse. :)

4. Mar 16, 2006

### matt grime

Rubbish, Jim: there are far too few symbols possible and far too meanings that need to be conveyed. Context makes it clear what is going on.

5. Mar 16, 2006

### arildno

Uniqe and fossilized use of symbols is counter-productive of developing flexibility of the mind. It is the definition AT HAND that matters, and if the chosen notation is convenient for its purpose.