Question

calculați sumele 1+2+3...+9+10

Answer 1

Suma Gauss:

$1+2+3+...+10= \frac{10\cdot11}{2}=55 \\ Forma\ generala: \\ 1+2+3+...+n= \frac{n(n+1)}{2}$

Answer 2

1+2+3+......+9+10=(1+10)+(2+9)+(3+8)+.....+(5+6)=11+11+11+.....+11=11*10/2= 110/2=55