2008/2009-2007/2008 通分：=(2008)/(2008×2009)-(2007×2009)/(2008×2009) =[2008-2007×2009]/(2008×2009) =[2008-(2008-1)×(2008+1)]/(2008×2009) 平方差公式：=[2008-2008+1]/(2008×2009) =1/(2008×2009)...