What is an example of direct proportionality?

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Discussion Overview

The discussion revolves around the concept of direct proportionality in mathematics, with participants seeking examples and clarifications regarding the conditions under which two variables are directly proportional.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant asks for an example of direct proportionality.
  • Another participant states that if y and x are directly proportional, then y = Ax, where A is a constant.
  • It is noted that this relationship can be represented as y ∝ x.
  • Concerns are raised about the value of A, with one participant suggesting that A should not be a positive constant less than 1 to avoid confusion with inverse proportionality.
  • Another participant challenges this assertion, stating that y and x remain directly proportional regardless of the value of A, as long as the relationship is defined as y = Ax.
  • A later reply acknowledges a misunderstanding regarding the conditions for direct proportionality.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the constant A in the context of direct proportionality, leading to some confusion and a lack of consensus on the conditions that define direct versus inverse proportionality.

Contextual Notes

There is ambiguity regarding the interpretation of the constant A and its impact on the relationship between y and x, particularly concerning values less than 1.

sotellme
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directly proportional? can anyone give an example of it?


thanks a lot!
 
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y and x are directly proportional, A is a constant.

y = Ax

\frac{y}{x} = A
 
Right. This is represented as y\propto x.
 
thanks! :smile:
 
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.
 
cyby said:
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.


hi cyby! what you mean with that? do you mean that A must always be a positve number if not it will be inversely proportional? :cry:
 
cyby said:
Careful. Make sure A is not a positive constant < 1. Otherwise you will get that they are inversely proportional.

No, that's not true. It's still a direct proportion. y and x are inversely proportional if y=A/x.
 
Uh, you are right. Sorry, was thinking about something else completely.
 

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