Triangle inequality in Rubins book

In summary, there is a problem given in which z and w are complex numbers. The goal is to prove the inequality ||z|-|w||\leq|z-w|\leq|z|+|w|. However, the person is confused because they believe that ||z|-|w||=|z-w| is true. They provide an example using z = -2 and w = 2, and ask if the statement still holds. They then mention their understanding of |z| as a length, but are unsure due to conflicting definitions in Rudin's book and their girlfriend's complex variables class.
  • #1
mynameisfunk
125
0
My problem states:
Given z, w[tex]\in[/tex]C, prove: ||z|-|w||[tex]\leq[/tex]|z-w|[tex]\leq[/tex]|z|+|w|.

Now, I am confused because, isn't it true that ||z|-|w||=|z-w| ? I am using Rudin's book which gives |z|=([z's conjugate]z)1/2
 
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  • #2
Take z =-2 and w = 2. Does ||z|-|w||=|z-w| still hold?
 
  • #3
Ah. Thank you. Is it correct from the definition of |z| to think of it as a length? My gf is taking a complex variables class and she had told me that |z|= the length of z, but rudin's book gave the definition above, so i didn't know how to think about it.
 

1. What is the Triangle Inequality in Rubins book?

The Triangle Inequality is a mathematical concept introduced by mathematician Ernst Kummer and further developed by mathematician Lawrence Rubins. It states that the sum of any two sides of a triangle must be greater than the third side.

2. Why is the Triangle Inequality important?

The Triangle Inequality is important because it helps in proving the existence and uniqueness of solutions in various mathematical problems, such as in optimization and geometry. It is also used in various fields like physics, computer science, and economics.

3. What are some real-life applications of the Triangle Inequality?

The Triangle Inequality has various applications in real-life scenarios, such as in engineering for designing structures that can withstand certain forces, in navigation for calculating the shortest distance between two points, and in economics for determining the feasibility of production processes.

4. How does the Triangle Inequality relate to other mathematical concepts?

The Triangle Inequality is closely related to the Pythagorean Theorem, as it is a special case of the Triangle Inequality for right triangles. It is also related to the Law of Cosines and the Law of Sines, which are used to solve triangles in trigonometry.

5. Are there any exceptions to the Triangle Inequality?

Yes, there are exceptions to the Triangle Inequality. It does not hold for non-Euclidean geometries, such as spherical or hyperbolic geometry. It also does not hold for degenerate triangles, where one or more sides have a length of zero.

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