原式
=(3/2)*(4/3)*(5/4)*……*(2006/2005)*(-1)^2005*(1/2)*(2/3)*……*(2005/2006)
=-1/2 *(3/2)*(2/3)*……*(2006/2005)*(2005/2006)
=-1/2
原式
=(3/2)*(4/3)*(5/4)*……*(2006/2005)*(-1)^2005*(1/2)*(2/3)*……*(2005/2006)
=-1/2 *(3/2)*(2/3)*……*(2006/2005)*(2005/2006)
=-1/2