Răspuns:
Explicație pas cu pas:
3 + 6 + 7 + 8 + 9 + ....... + 105 = 5 553
= ( 1 + 2 + 3 + 4 + .... + 105 ) - ( 1 + 2 + 4 + 5 ) =
= 105 × ( 1 + 105 ) : 2 - 12 =
= 105 × 106 : 2 - 12 =
= 105 × 53 - 12 =
= 5 565 - 12 =
= 5 553
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Sau:
3 + ( 6+7+8+9+.....+ 105) =
= 3 + ( 105 - 6 + 1 ) × (6+105):2 =
= 3 + 100 × 111 : 2 =
= 3 + 50 × 111=
= 3 + 5 550 =
= 5 553