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Question Number 28833 by abdo imad last updated on 30/Jan/18

l e t g i v e φ (x) = x, φ 2 π p e r i o d i q u e e v e n

d e v e l o p p f a t f o u r i e r s e r i e s t h e n f i n d t h e v a l u e o f

\sum_{n = 1}^{\infty} \frac{{(- 1)}^{n}}{n^{2}} a n d \sum_{n = 0}^{\infty} \frac{1}{{(2 n + 1)}^{2}} .