[tex]\underline {Suma~Gauss}: 1+2+3+...+n=[n \cdot (n+1)]:2 [/tex]
[tex] = \{[2012 \cdot (2012 + 1)] :2 \} \cdot [ \frac{1}{2012} - ( \frac{1}{2012} - \frac{1}{2013} ] = \\ \\
=[(2012 \cdot 2013):2] \cdot (\frac{1}{2012}-\frac{1}{2012}+\frac{1}{2013})= \\ \\
\frac{2012 \cdot 2013}{2} \cdot \frac{1}{2013}= \frac{2012}{2}=1006 [/tex]
