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Can you explain to me why

[tex](1-1+1-1...)=\sum_{n=0}^{\infty}(-1)^n=\frac{1}{2}[/tex]

and

[tex](\frac{1}{1^2}+\frac{1}{2^2}+\frac{1}{3^2}...)=\sum_{n=1}^{\infty}\frac{1}{n^2}=\frac{\pi ^2}{6}[/tex]

I don't understand these equalities.Thanks.

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# Euler's equalities

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