2009 + 2008 + 2007 + 2006 + 2005 +2004 + 2003 +2002 + ...+3 +2 +1等于?
问题描述:
2009 + 2008 + 2007 + 2006 + 2005 +2004 + 2003 +2002 + ...+3 +2 +1等于?
答
2009 + 2008 + 2007 + 2006 + 2005 +2004 + 2003 +2002 + ...+3 +2 +1
=(2009+1)×2009÷2
=2019045