Help proving triangle inequality for metric spaces

In summary, the conversation discusses the proof of the triangle inequality for the distance formula, specifically for the fractions Xk-Zk and Zk-Yk. The approach of transforming the denominator is suggested, but there is uncertainty about its validity. The conversation also touches on the idea of using the function x/(1+x)=1-1/(1+x) to prove a specific case of |a-b+b-c| = |a-b| + |b-c|.
  • #1
lucasLima
17
0
So, i need to proof the triangle inequality ( d(x,y)<=d(x,z)+d(z,y) ) for the distance below
5XzC654.jpg

But I'm stuck at
S6sjolB.jpg


In those fractions i need Xk-Zk and Zk-Yk in the denominators, not Xk-Yk and Xk-Yk. Thanks in advance
 
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  • #2
a/(1+a) = 1 - 1/(1+a)
Then you just have to transform the denominator and not both parts. Not sure if that is the best approach, but it is the one I would try first.
 
  • #3
I used somthing similar instead Minkowski, i did (a+b)/(1+a+b) <= a/(1+a) + b/(1+b)
0Ko8ooz.jpg
f
 
  • #4
I don't think that is a valid transformation with the denominator. You change 1+|g+f| to 1+|g|+|f| which might increase the fraction.
 
Last edited:
  • #5
mfb said:
I don't think that is a valid transformation with the denominator. You change 1+|g+f| to 1+|g|+|f| which might reduce the fraction.
But in that case g and f are > 0, so in no way will reduce the fraction. |g|+|f|>|g+f| only if g or f is <0
 
  • #6
You don't know that about f and g (which are the raw differences, e.g. xk-zk).

"reduce" in the last post should be "increase", of course.
 
  • #7
(Thank you for all your help s far) What if i told you that |a-b+b-c| = |a-b| + |b-c|? I'm having a little trouble prooving that but I'm pretty confident.
 
  • #8
Not in general.

a=2, b=5, c=1
1 = 3 + 4?
 
  • #9
You should use the fact that the function x/(1+x)=1-1/(1+x) is increasing.
 

1. What is the triangle inequality for metric spaces?

The triangle inequality for metric spaces is a mathematical concept that states that the sum of any two sides of a triangle must be greater than the length of the third side. This applies to any metric space, which is a set of objects with a defined distance function between them.

2. Why is the triangle inequality important in metric spaces?

The triangle inequality is important in metric spaces because it helps to define the concept of distance between objects in a mathematical way. It also ensures that the distance function in a metric space satisfies certain properties, such as the triangle inequality, which is essential for many mathematical proofs and applications.

3. How can I prove the triangle inequality for metric spaces?

The triangle inequality can be proved using different methods, depending on the specific metric space and distance function being considered. Generally, it involves using mathematical properties and definitions to show that the sum of any two sides of a triangle is always greater than the length of the third side. This can be done using algebraic manipulations, geometric reasoning, or other mathematical techniques.

4. What are some real-world examples of the triangle inequality in metric spaces?

The triangle inequality is a fundamental concept in mathematics that has many real-world applications. For example, it is used in geometry to prove geometric theorems and solve problems involving triangles. It is also used in physics to describe the relationship between distance, time, and speed. In computer science, it is used in algorithms for shortest path calculations and clustering.

5. Are there any variations of the triangle inequality for metric spaces?

Yes, there are several variations of the triangle inequality that apply to different types of metric spaces. For example, there is a generalized triangle inequality for metric spaces with multiple points, and a reverse triangle inequality for metric spaces with negative distances. These variations may have different mathematical formulations, but they all serve the same purpose of defining the relationship between distances in a metric space.

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