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$ f(x) + f(x + a) = c$

where $a$ and $c$ are known constants and $f$ is the function of interest.

I understand that if one of the two terms on the LHS involved a derivative, then we would face a delayed differential equation ... but being short of a derivative, I don't even know how to call it (yet alone solve for it).

bonifaz
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1 Answers1

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[As requested, made into an answer]

You could call it a functional equation. More particularly, a first-order constant-coefficient linear nonhomogeneous difference equation.

Robert Israel
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