\(S=2+\left(-3\right)+4+\left(-5\right)+...+2014+\left(-2015\right)\)
\(\Rightarrow S=\left[2+\left(-3\right)\right]+\left[4+\left(-5\right)\right]+...+\left[2014+\left(-2015\right)\right]+2016\)( 1007 cặp số )
\(\Rightarrow S=\left(-1\right)+\left(-1\right)+...+\left(-1\right)+2016\) ( 1007 số -1 )
\(\Rightarrow S=-1007+2016\)
\(\Rightarrow S=1009\)