Question

Calculati;1+2+3+....+9+10=?​

Answer 1

$\it 1+2+3+\ ...\ +n=\dfrac{n(n+1)}{2}\\ \\ \\ 1+2+3+\ ...\ +10=\dfrac{10\cdot11}{2}=5\cdot11=55$

$\it 1+2+3+\ldots +n=\dfrac{n(n+1)}{2}\ \ \ Foemula\ lui\ Gauss$