Does x ≤ ky Imply x < y for k < 1 in Mathematical Analysis?

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Discussion Overview

The discussion revolves around the implications of the inequality \( x \leq ky \) for \( k < 1 \) and whether it necessarily leads to \( x < y \) for positive real numbers \( x \) and \( y \). Participants explore this concept within the context of mathematical analysis, particularly in relation to Lipschitz transforms and contraction mappings.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Jesse questions whether the statement \( \exists k<1 \,\, s.t. \,\, x \leq k\cdot y \, \Leftrightarrow \, x
  • One participant asks if \( k \) is also a positive real number, clarifying that \( 0 < k < 1 \).
  • Another participant suggests visualizing the situation on an xy-plane to understand the relationship between the lines \( x = y \) and \( x = ky \).
  • A different viewpoint is presented, arguing that if \( k \) can be made arbitrarily close to 1, then \( x \leq k \cdot y \) could approach \( x < y \), raising questions about the implications of \( k \) being close to 1.
  • One participant provides a reasoning process, stating that if \( k < 1 \), then multiplying both sides of \( x < ky \) by \( y \) leads to \( x < y \), and conversely, if \( x < y \), there exists a \( k < 1 \) such that \( x < ky \).

Areas of Agreement / Disagreement

Participants express differing views on the implications of the inequality, with some supporting the idea that \( x < y \) follows from \( x \leq ky \) for \( k < 1 \), while others question the validity of this implication. The discussion remains unresolved, with no consensus reached.

Contextual Notes

Participants note the importance of the conditions under which the inequalities hold, particularly the role of \( k \) being less than 1 and the positivity of \( x \) and \( y \). There are also considerations regarding the behavior of \( k \) as it approaches 1.

tragicmuffin
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I have a question on something that has come up many times for me in other contexts, such as Lipschitz transforms, and recently contraction mappings and the fixed point theorem.

Is the following statement always false, and why?

Let x and y be two positive real numbers.
\exists k&lt;1 \,\, s.t. \,\, x \leq k\cdot y \, \Leftrightarrow \, x&lt;y

So far, I've always seen statements like this to be false, but I'm not sure why.

Thanks,
Jesse
 
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Sorry, yes. 0<k<1.
 
I can't say if its true or not but try to visualize it on a xy plane where the area under the line x=y is x<y versus the line x=ky.

Perhaps that will help you decide.
 
I guess the thing that I don't understand is that if k is strictly less than 1, can't we still make k as close to 1 as we want? Then wouldn't saying x \leq k \cdot y where k is arbitrarily close to 1 (but not equal) be the same as saying x&lt;1 \cdot y?
It seems to me that changing the \leq to &lt; would account for k not being equal to 1, only close.

In the example with the lines, the same idea would hold. We can make k arbitrarily close to 1, and thus make the line x=ky arbitrarily close to the line x=y.
 
tragicmuffin said:
I have a question on something that has come up many times for me in other contexts, such as Lipschitz transforms, and recently contraction mappings and the fixed point theorem.

Is the following statement always false, and why?

Let x and y be two positive real numbers.
\exists k&lt;1 \,\, s.t. \,\, x \leq k\cdot y \, \Leftrightarrow \, x&lt;y

So far, I've always seen statements like this to be false, but I'm not sure why.

Thanks,
Jesse
If k< 1 then, mutiplying both sides by the positive number y, ky< y. So if x< ky, it is certainly true that x< y.

Conversely, if x< y, then x/y< 1 and so there exist k such that x/y< k< 1. That is, we have k< 1 and, multiplying both sides of x/y< k, x< ky.
 

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