Monday
October 20, 2014

Homework Help: Math

Posted by Rosanna on Tuesday, September 19, 2006 at 9:38pm.

For homework we're supposed to give all the properties of different functions. I was able to do all of it except for this one greatest integer function -

f(x) = -1/2 [x-1]

These functions always mess me up!

Could someone tell me the following properties of this function.

Increasing Intervals
Decreasing Intervals
1-1?
Continuity
End-Behavior
Boundedness
Asymptotes
x-intercept (s)
y-intercept

Thanks I appreciate it a ton!!!!



The greatest integer or step function does require careful handling. You should graph the function f(x)=[x] and make sure you understand what the function looks like.

[x] on [-2,-1)=-2
[x] on [-1,0)= -1
[x] on [0,1)=0
[x] on [1,2)=1
Graph this for a few more values to understand the basic step function.

Now look at
f(x)=-1/2 [x-1]
f(x) on [-2,-1)=3/2
f(x) on [-1,0)= 1
f(x) on [0,1)=1/2
f(x) on [1,2)=0
f(x) on [2,3)=-1/2
f(x) on [3,4)=-1

Increasing intervals? Do you see any?
Decreasing Intervals Kind of tricky, but check that f(x) is monotonic decreasing on it's domain. I hope you're familiar with the terms.
1-1? If you can find two x values with the same f(x) value on an interval it's not 1-1.
Continuity If you restrict yourself to the interval [z,z+1) where z is any integer then it's continuous.
End-Behavior Is it continuous at the endpoints?
Boundedness Consider any interval I, it can be open, closed or mixed. Does f(x) have a min and max on I?
Asymptotes The answer should be self-evident if you graph a few intervals. Are there any vertical, horizontal or oblique asymptotes anywhere?
x-intercept Check where f(x)=0.
y-intercept Check the interval that contains x=0.

Be sure you know the basic step function. This function is widely used in economics and areas of applied math where we want only integer solutions.
Now check my calulations and explanations.



Ok I'm not sure, but then could you check my answers for these properties for the same function?

Increasing and decreasing intervals - None?
1-1 - No?
Continuity - No?
End Behavior - ?
Boundness - No?
Asymptotes - No?
x-intercept - (0,1/2)
y-intercept - (1.9,0)


Increasing and decreasing intervals - None? Correct about increasing, but technically this is a monotonic decreasing function. It's not strictly monotonic decreasing, so I'm not sure how your text is using the term decreasing.
1-1 - No? Correct
Continuity - No? Not continuous for the integers. Continuous for all other reals.
End Behavior - ? Discontinuous for the integers, because for an integer n from the right it is (-1/2)(n-1) and from the left it's (-1/2)(n-2).
Boundness - No? f(x) is bounded for every interval except any that has +/-infinity describing it. I see no domain was specified, so we should suppose the largest possible domain is meant and that would be (-infintity, infinity) and thus f(x) is not bounded on R. the reals.
Asymptotes - No? Correct
x-intercept - (0,1/2) No, Check the table I gave. What interval has f(x)=0?
y-intercept - (1.9,0) No " " " " Find the interval that has x=0 in it and check it's f(x) value.

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