Question

calculați 3 plus 6 plus 9 plus puncte puncte plus 90
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Answer 1

Răspuns:

1395

Explicație pas cu pas:

Salut! (●'◡'●)

$3+6+9+...+90=$

Dam factor comun pe 3. Obtinem:

$3(1+2+3+...+30)=$

Folosim suma Gauss:

$3\cdot \frac{30\cdot31}{2}\\\\3\cdot 15\cdot31\\\\45\cdot31\\\\\underline{1395}$

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