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1+3+5+71...+75
3+6+9+12+...+99
5+101+15+20+...+2005
15pct repede pls

Răspuns :

Antonia388
1)
1+3+5+....+73+75=
(2x0+1)+(2x1+1)+(2x2+1)+...+(2x36+1)+(2x37+1)=
2(0+1+2+...+36+37)+1x38=
2x37x38/2+38=
37x38+38=38(37+1)=38x38

2)
3(1+2+3+...+33)=
   3x33x34/2=1683

3)
5(1+2+3+...+401)=
5x401x402/2=403 005

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