Is this a differential equation?

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Discussion Overview

The discussion centers around the definition of a differential equation, specifically questioning whether the equation y' = 3x² qualifies as a differential equation given that the original function y does not appear explicitly in the equation.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant cites a textbook definition stating that a differential equation contains both the function and its derivative, questioning the validity of this definition in the case of y' = 3x².
  • Another participant argues that y' = 3x² can be rewritten in forms that include the function y, suggesting that the textbook's definition may be overly strict and that definitions can evolve with learning.
  • A third participant asserts that while y' = 3x² is a differential equation, the statement about the function needing to be present is misleading, as the derivative must appear explicitly but the function itself does not need to be.

Areas of Agreement / Disagreement

Participants express differing views on the definition of a differential equation and whether the function must be explicitly included. There is no consensus on the interpretation of the textbook definition.

Contextual Notes

The discussion highlights potential ambiguities in definitions and the evolution of understanding in mathematics, particularly regarding the inclusion of functions in differential equations.

johann1301
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My textbook says that:

"A differential equation contains both the function and the derivative of the function"

and at the same time claims that y'=3x2 is a differential equation.

How can this be? The original function isn't part of the equation in this case?
 
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Yes it is. y'=3x2 is the same as y'+0y=3x2 (the coefficient of y is zero) and also the same as:
xy'=3y

But I think you need to take the textbook a little less seriously.
What they mean is that if g(x)=f(x,y,y',y''...) then g is a DE.
As you learn more the definition will get expanded to include more cases.
 
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It is a particularly easy differential equation- y is simply the anti-derivative of [tex]3x^2[/tex]. I would say the statement "A differential equation contains both the function and the derivative of the function" is at best misleading. The derivative of the function must appear explicitly in the equation. The function itself does not have to be explicitly in the equation.
 
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Thanks!
 

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