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Calulati suma S=7+7la2+7la3+...+7laputerea2003-7la1
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Răspuns :

Sn=7+7^2+7^3+........+7^2003 |7

7Sn=7^2+7^3+............+7^2004
scăzând sumele
7Sn-Sn=(7^2004-7)
6Sn=(7^2004-7)
Sn=(7^2004-7)/6
S=Sn-7
S=7^2004-7-6×7
S=7^2004-7(1+6)
S=7^2004-7^2
S=7^2(7^2002-1)