Question

ma puteți ajuta?până mâine​

Answer 1

1) s=1+2+3...+99

1+2+3+...+99=99×(99+1):2=99×100:2=9900:2=4950

2)s=1+2+3+...+105

1+2+3+...+105=105×(105+1):2=105×106:2=11130:2= 5565

3) s=1+2+3+...+120

1+2+3+....+120=120×(120+1):2=120×121:2=14520:2= 7260

4)s=1+2+3+...+250

1+2+3+...250=250×(250+1):2=250+251:2=62750:2= 31375

5)1+2+3+...+399

1+2+3+...+399=399×(399+1):2=399×400:2=159600:2= 79800

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Formula:

1+2+3+...+n=n(n+1):2