Question

（+1）+（-3）+（+5）+（-7）.+（+2005）+（-2007）+（+2009）+（-2011）=

Answer 1

原式

= (1 - 3) + (5 - 7) + ...+ (2005 - 2007) + (2009 - 2011)

= (-2) + (-2) + ...+ (-2) + (-2)

= (-2) × 503

= -1006