Question

dau coroana gauss va rog ​

Answer 1

[n×(n+1)]:2

1+2+3+...+86=[86×(86+1)]:2

=(86×87):2

= 86:2×87=43×87=3741

1+2+3+...+102=(102×103):2

=51×103

=5253

1+2+3+...+62=(62×63):2

=31×63

=1953

1+2+3+...+1000=(1000×1001):2

=500×1001

=500500

1+2+3+...+120=(120×121):2

=60×121

=7260