Find the supremum, infinum, maximum and minimum

In summary, the problem is to find the supremum, infimum, maximum and minimum of the function (n-2sqrt(n)), where n is an element of natural numbers. One approach suggested is to draw the graph of the function and use the definition of sup, inf, max and min. Another suggestion is to find the critical points of the related function f(x) = x - 2sqrt(x) for real numbers and then restrict the answer to natural numbers. This would also help in determining when the function is increasing or decreasing.
  • #1
joshuamcevoy
2
0

Homework Statement



find the supremum, infinum, maximum and minimum

Homework Equations


(n-2sqrt(n)) n is element of natural numbers


The Attempt at a Solution


no idea on how to do this help please
 
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  • #2


Drawing the graph is always a good idea. You know the graph of y=x and i assume also the graph of 2*x^1/2. After that you can easily sketch x-2*x^2 and then you'll probably have a better idea were to look
 
  • #3


Do you know the definition of sup, inf, max and min, or is it just this question in particular that is causing problems?
 
  • #4


its this question in particular that's giving me the headache
 
  • #5


Well, what is the smallest natural number? What is the value of the function at that point? Does the function increase or decrease from that point? Does it converse or diverge?
 
  • #6


joshuamcevoy said:

Homework Equations


(n-2sqrt(n)) n is element of natural numbers

Why don't you try finding the critical points for the related function [itex] f(x) = x - 2 \sqrt{x}[/itex] for real numbers and then restricting your answer to the naturals? This would also provide you with an easy way to use Disconnected's idea of examining when the function is increasing and decreasing.
 

1. What is the difference between supremum and maximum?

The supremum, also known as the least upper bound, is the smallest number that is greater than or equal to all elements in a set. The maximum, on the other hand, is the largest number in a set. In some cases, the supremum and maximum may be the same value, but this is not always the case.

2. How is the infimum different from the minimum?

Similar to the supremum and maximum, the infimum and minimum have subtle differences. The infimum, or greatest lower bound, is the largest number that is less than or equal to all elements in a set. The minimum, on the other hand, is the smallest number in a set. Again, they may be the same value in some cases, but not always.

3. How do you find the supremum and infimum of a set?

To find the supremum and infimum of a set, you first need to list out all the elements in the set. Then, you can compare them and determine the largest and smallest values. The supremum will be the smallest value that is greater than or equal to all elements, and the infimum will be the largest value that is less than or equal to all elements.

4. Is it possible for a set to have no supremum or infimum?

Yes, it is possible for a set to have no supremum or infimum. This occurs when the set is unbounded, meaning there is no upper or lower limit. For example, the set of all positive numbers has no infimum, as there is no largest number that is less than or equal to all elements in the set.

5. What is the significance of finding the supremum and infimum of a set?

Finding the supremum and infimum of a set is important in mathematical analysis and optimization problems. It allows us to define upper and lower bounds for a set, which can help us determine the behavior and limits of a function or system. It also helps us identify the maximum and minimum values within a set, which can be useful in decision making and problem solving.

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