Răspuns:
Explicație pas cu pas:
1+2-3+4+5-6+7+8-9+... +2005+2006-2007+2008=(1+2-3)+(3+3-3)+(1+2-3)+(6+6-6)+(1+2-3)+...+(2004+2004-2004)+(1+2-3)+2008=0+3+0+6+...+2004+0+2008=3·(1+2+3+...+668)+2008=3·668·669:2+2008=3·334·669+2008=334·2007+2008=334·2007+2007+1=2007·335+1=672346