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Calculatii: .... 
Multumesc.


Calculatii Multumesc class=

Răspuns :

[tex] \frac{4}{1\cdot5} + \frac{4}{5\cdot9}+...+ \frac{4}{2013\cdot2017}=\\ = \frac{1}{1}- \frac{1}{5} + \frac{1}{5}- \frac{1}{9} +...+ \frac{1}{2013}- \frac{1}{2017} =\\ =\frac{1}{1}-\frac{1}{2017}=\\ = \frac{2016}{2017} [/tex]