2009又1/2+(-2010又5/6)+(-2011又2/3)+2012又1/3+(-1又1/2)
=(2009又1/2-1又1/2)+(2012又1/3-2011又2/3)-2010又5/6
=2008+2/3-2010又5/6
=2008又4/6-2010又5/6
=-2又1/6