1/（2/3）/（3/4）/（4/5）./（2009分之2008）
=1/[(2/3)*(3/4)*(4/5)*...*(2008/2009)]
=1/(2/3*3/4*4/5*...*2008/2009)
=1/(2/2009)
=1*2009/2
=2009/2