Question

formula la 1+2+3+4........+69=

Answer 1

1+2+3+4+...+n=n(n+1)/2

in cazul tau

1+2+3+4+...+69=69*70/2=2415

Answer 2

$\displaystyle \boxed{1+2+...+n= \frac{n(n+1)}{2} } \\ \\ 1+2+3+4+...+69= \frac{69(69+1)}{2} = \frac{69 \times 70}{2} = \frac{4830}{2} =2415$