Question

2+4+6+.......+40. 3+6+9+.........+102. 4+8+12+.......+136 dau corona ​

Answer 1

Răspuns:

2+4+6+....+40=2·(1+2+3+....+20)=2·(20·21/2)=20·21=420

3+6+9+.....+102=3·(1+2+3+....34)=3·(34·35/2)=3·595=1785

4+8+12+...+136=4·(1+2+3+...+34)=4·(34·35/2)=4·595=2380

sume gauss

1+2+3+....+n=n·(n+1)/2

Explicație pas cu pas: