\(a)\, S = (1 - 2) + (3 - 4) + ... +\)\( (2009 - 2010)\)
\(=\underbrace {(-1) + (-1) + ... + (-1)}_{1005 \,số \,hạng}\)
\(= (-1)\,.\,1005 = -1005\)
\(b)\, P = (0 - 2) + (4 - 6) + ... +\)\( (2010 - 2012)\)
\(=\underbrace {(-2) + (-2) + ... + (-2)}_{503 \,số \,hạng}\)
\(= (-2)\,.\,503 = -1006\)
