Question

Calculati 7 +8+9+......+310 =

Answer 1

7+8+9+....+310=
=(1+2+3+....+310)-(1+2+3+....+6)=
=(310*311:2)-(6*7:2)=
=155*311-3*7=
=48205-21=48184

Answer 2

[tex]7+8+9+...+310\\ (1+2+3+4+5+6+...+310)-(1+2+...+6)\\ Doua~sume~Gauss,in~ambele~aplicam:[n(1+n)]:2\\ =\ \textgreater \ \frac{310*311}{2} - \frac{6*7}{2} =\ \textgreater \ 48205-21=48184[/tex]