\(\left(x_1+x_2+x_3\right)+\left(x_4+x_5+x_6\right)+...+\left(x_{1999}+x_{2000}+x_{2001}\right)+x_{2002}=0\)
\(\Rightarrow1+1+1+...+1+x_{2002}=0\)
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\(\frac{\left(2001-1+1\right)}{3}\)số 1
\(667+x_{2002}=0\)
\(x_{2002}=-667\)