If a sum is 0, is the summand 0?

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Discussion Overview

The discussion revolves around the mathematical question of whether a summand must be zero if the sum of several terms equals zero. Participants explore a specific equation involving summation and variables, seeking to understand how to approach solving it, particularly in relation to the values of certain parameters.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • Some participants propose that a sum equaling zero does not necessitate that each individual term is zero, citing examples where positive and negative terms can cancel each other out.
  • One participant asks for clarification on which variables are being solved for and what represents known values, indicating a need for more context.
  • Another participant presents a more complex equation and expresses a desire to solve for specific parameters, alpha and beta, one at a time.
  • There is a clarification regarding the variables involved in the equation, with one participant correcting their earlier statement about the summation.
  • One participant notes that the derived equation does not yield a unique solution and suggests that additional equations may be necessary to find unique values for alpha and beta.
  • A later reply acknowledges a misunderstanding about the variables involved and indicates that the issue has been resolved with the help of others.

Areas of Agreement / Disagreement

Participants generally agree on the idea that a sum can be zero without all summands being zero, but there is no consensus on the specifics of solving the equations presented, as multiple approaches and interpretations are discussed.

Contextual Notes

Some limitations include the need for additional equations to achieve unique solutions for the parameters alpha and beta, as well as the dependence on the interpretation of the variables involved in the summation.

Dixanadu
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Hey guys,

Was just wondering something. Suppose I have an equation of the form

[itex]\sum_{i=0}^{n}\frac{1}{x_{i}}(a-by_{i})=0[/itex],

how would I solve this? do I just set the summand = 0?
 
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Dixanadu said:
Hey guys,

Was just wondering something. Suppose I have an equation of the form

[itex]\sum_{i=0}^{n}\frac{1}{x_{i}}(a-by_{i})=0[/itex],

how would I solve this? do I just set the summand = 0?
No. If the terms in the sum can be positive or negative, their sum can be zero without any of them being zero. As a simple example, 2 + (-1) + (-1) = 0, but no single term equals zero.
 
Last edited:
Dixanadu said:
how would I solve this?
What variables are you solving for? What symbols represent known values ?
 
The real equation I'm dealing with is
[itex]\sum_{i=1}^{n}\frac{1}{\sigma_{i}^{2}}2x(y_{i}-\alpha x -\beta x^{2})=0[/itex]

and I am trying to solve for alpha and beta but one at a time...
 
Dixanadu said:
The real equation I'm dealing with is
[itex]\sum_{i=1}^{n}\frac{1}{\sigma_{i}^{2}}2x(y_{i}-\alpha x -\beta x^{2})=0[/itex]

So it's "[itex]x[/itex]" instead of "[itex]x_i[/itex]"?`
 
Yes I wrote it completely differently in the original post as I didnt think I would need to put the actual equation here but I changed my mind, sorry.

There is no summation over [itex]x[/itex], only over the [itex]\sigma_{i}[/itex] and [itex]y_{i}[/itex].
 
The closest I can get is

[itex](\alpha x +\beta x^{2})\sum_{i=1}^{n}\frac{1}{\sigma_{i}^{2}}=\sum_{i=1}^{n}\frac{y_{i}}{\sigma_{i}^{2}}[/itex]

No idea what to do from here
 
Dixanadu said:
The closest I can get is

[itex](\alpha x +\beta x^{2})\sum_{i=1}^{n}\frac{1}{\sigma_{i}^{2}}=\sum_{i=1}^{n}\frac{y_{i}}{\sigma_{i}^{2}}[/itex]

No idea what to do from here

That equation doesn't have a unique solution. To get a unique solution, you need to know another equation involving [itex]\alpha[/itex] and [itex]\beta[/itex].

Does this equation come from setting a partial derivative equal to zero? If so, perhaps there is another partial derivative that's supposed to be set equal to zero.
 
Yes you are right - it turns out that the [itex]x[/itex] are also summed in addition to [itex]y_{i},\sigma_{i}[/itex], i had interpreted the situation inocorrectly.

Everything is fine now thank you for your help! :D
 

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