Question

1+3+5+12+14+16 =?

1+2+3+4+5+...+50

2+4+6+....+60

3+6+9+12+....+99

5+10+15+....+2005

Answer 1

Răspuns:

1+3+5+12+14+16=51

1+2+3+4+5+..+50=(50x51):2=1275

2+4+6+...60=2(1+2+3+..+30)=6((30x31):2)=6x465=2790

3+6+9+12+...+99=3(1+2+3+...+33)=3((33x34):2)=3x561=1683

5+10+15+...+2005=5(1+2+3+...+401)=5((401x402):2)=5x80601=403005

Explicație pas cu pas: