Question

1+2+3+4+5+6+7+8+9=
Dau coroana​

Answer 1

$\displaystyle\bf\\Aplicam~ formula~ lui~ Gauss.\\\\1+2+3+4+5+6+7+8+9=\frac{9(9+1)}{2}=\frac{9\times10}{2}=\frac{90}{2}=\boxed{\bf45}$

 

 

Answer 2

Salutare!

$1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = (1 + 9) + (2 + 8) + (3 + 7) + (4 + 6) + 5 = \\ 10 + 10 + 10 + 10 + 5 = \\ 20 + 10 + 10 + 5 = \\ 30 + 10 + 5 = \\ 40 + 5 = \\ 45$