Linear relationship at small x

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    Linear Relationship
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Discussion Overview

The discussion revolves around the concept of linear relationships in the context of Taylor and Maclaurin series expansions, particularly focusing on how these expansions behave for small values of x. Participants explore whether an equation can be considered linear based on its series expansion and the implications of such approximations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about how to demonstrate a linear relationship for small x and whether the ability to Taylor expand an equation implies linearity.
  • Another participant suggests that a linear function can approximate a given function by ignoring higher degree terms in the Taylor or Maclaurin series, using the example of e^x.
  • A query is raised regarding the status of a Maclaurin expansion that results in terms only of a0, a2, and a3, questioning if it can still be considered linear.
  • It is proposed that the best linear approximation at x = 0 is a0, which represents a horizontal line due to the derivative being zero at that point.
  • One participant asserts that including x^2 and x^3 terms in the expansion means the equation cannot be classified as linear.
  • Another participant discusses the implications of approximating to a0, suggesting that for small x, the function behaves as a constant, leading to the question of whether it indicates that the function is not dependent on x.

Areas of Agreement / Disagreement

Participants express differing views on the classification of linearity in relation to the presence of higher-order terms in series expansions. There is no consensus on whether an equation can be considered linear if it includes terms beyond the constant.

Contextual Notes

The discussion highlights the ambiguity in defining linearity based on series expansions and the role of derivatives at specific points, with various assumptions about the behavior of functions near x = 0 remaining unresolved.

watertreader
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in general, how do we show linear relationship over a small x of the equation?

Is the equation being able to be Taylor expand show itself as linear? likewise can we consider the series expansion at about x=0 (maclaurin series) to be linear too?


If not, is there any examples countering the above notion? appreciate if anyone can point out to how to substantiate an equation to be linear at small x?

thanks
 
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You can use a linear function to approximate a given function by ignoring all terms of degree two and higher in the Taylor or Maclaurin series.

For example, the Maclaurin series for e^x is 1 + x + x^2/2! + ... The linear approximation, for small x (x close to 0) is y = 1 + x.
 
just another query...if we have done a Maclaurin expansion on an equation ...the result is a0 + a2x^2 + a3 x^3 +...

does it still qualify to say that the equation is still linear? since the only terms in the expansion up to x terms are only a0

thankls
 
In this one might say the best linear (more precisely affine) approximation at x = 0 is just a0, a horizontal line. This is because the derivative of the function at 0 is zero.
 
watertreader said:
just another query...if we have done a Maclaurin expansion on an equation ...the result is a0 + a2x^2 + a3 x^3 +...

does it still qualify to say that the equation is still linear? since the only terms in the expansion up to x terms are only a0

thankls
No, that is not linear if you are including the x2 and x3 terms.
 
Tedjn said:
In this one might say the best linear (more precisely affine) approximation at x = 0 is just a0, a horizontal line. This is because the derivative of the function at 0 is zero.

so if we take an approximation to a0, even if we made a small change to x, we will still obtain a straight line or a constant

Would this suggest that at small x, the function itself is not a function of x?

thanks
 
For small x, y = a0 is a constant function of x.
 

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