Proof or Counterexample on Fourier Series for a_n=0

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The discussion centers on the implications of the equation \(\sum_{n=0}^\infty a_n \, g_n(x) = 0\) in relation to Fourier series. It concludes that \(a_n\) does not necessarily equal zero for all \(n\) unless the basis functions \(g_n\) are mutually orthogonal. A comparison is made to the product \(f(x) g(y) = 0\), which only requires that each function be a constant. The key takeaway is the importance of linear independence in determining the coefficients \(a_n\).

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ghotra
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Actually this might not be a Fourier question, but it certainly reminds of Fourier series.

Suppose,

<br /> \sum_{n=0}^\infty a_n \, g_n(x) = 0<br />

Does it necessarily follow that a_n = 0 \: \forall n? If so, please provide a proof. If not, a counterexample would be helpful. If not, can I deduce anything about the the coefficients?

A similar formula,
<br /> f(x) g(y) = 0<br />

only implies that each function must be a constant.
<br /> \sum_n f_n(x) \, g_n(y) = 0<br />
Under a sum, my guess is that we can't say anything about each of the functions.
 
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The a_n will necessarily be zero only if the basis functions g_n are mutually orthogonal (linearly independent).
 
Haha! I knew I had seen that sum before! Independence!

lol...thanks.
 

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