Question

Calculati : A)
3+6+9+....+33 B) 10+20+30+....+1250
Cine stie sa imi explice cum se face ii dau coroana

Answer 1

A) 3 + 6 + 9 + ... + 33 =

3×1 + 3×2 + 3×3 +...+ 3×11 =

3 × (1 + 2 + 3 +...+ 11) =

3 × 11 × (11 + 1) : 2 =

3 × 11 × 12 : 2 =

33 × 6 =

198


B) 10+20+30+....+1250 =

10×1 + 10×2 +10×3 + ... + 10×125 =

10 × (1 + 2 + 3 +...+ 125) =

10 × 125 × (125 + 1) : 2 =

10 × 125 × 126 : 2 =

1 250 × 63 =

78 750


La ambele exercitii am dat factor comun, apoi am calculat cu ajutorul Sumei lui Gauss .