Question

Cat este suma numerelor 1+2+3+....+2006

Answer 1

S= 2006*2007 / 2 
S=1003*2007
S=2013021

Answer 2

$\displaystyle \boxed{ \frac{n(n+1)}{2} } \ \text{n este ultimul numar din sir} \\ \\ \\ \frac{2006(2006+1)}{2}= \frac{\not2006 \cdot2007}{\not2} \\ \\ \\ 1003\cdot2007=2013021$