Care este suma ?

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miruna.lazar
Bernoulli
Posts: 224
Joined: Wed Oct 08, 2008 8:41 pm
Location: Tulcea

Care este suma ?

Post by miruna.lazar »

Aflati suma : 5 + 10 + 15 ... + 355 .
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alex2008
Leibniz
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Joined: Sun Oct 19, 2008 3:23 pm
Location: Tulcea

Post by alex2008 »

\( 5+10+15+...+355=5(1+2+3+...+71)=5\cdot\frac{71\cdot72}{2}=12780 \)
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