2006×2007+2007×2008+2006×2008?2 1+2+3+…+2006+2007 = 2006×(2008?1)+(2006+1)×2008+2006×2008?2 (1+2007)×2007÷2 = 2006×2008?2006+2006×2008+2008+2006×2008?2 2008×2007÷2 = 2006×2008×3 2008×2007÷2 = 4012 669 ．
