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# Functional Functions that Function

Find all functions $$f : \mathbb{R} \rightarrow \mathbb{R}$$ such that $$f (x + y) + 2f (x - y) + f (x) + 2f (y) = 4x + y$$ for all real $$x$$ and $$y$$.

Note by Yuxuan Seah
2 years, 9 months ago

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SORRY, I MISTYPED IN THE FIRST LINE,f(x)=0 but it is f(x)=x · 2 years, 9 months ago