I am trying to understand how to calculate the sum of the following(adsbygoogle = window.adsbygoogle || []).push({});

infinite series, can someone help please:

(5/7)^{2}- (5/7)^{3}+ (5/7)^{4}- (5/7)^{5}+ ...

The sum of such a series should be given by:

a / (1-r)

But the value of a = 0 (the first term = 0), hence my confusion.

Thanks

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# Sum of infinite series

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