(1-1/2)(1/3-1)(1-1/4)(1/5-1)…(1/2003-1)(1-1/2004)

(1-1/2)(1/3-1)(1-1/4)(1/5-1)…(1/2003-1)(1-1/2004)
=(1-1/2)(1-1/3)(1-1/4)(1-1/5)…(1-1/2003)(1-1/2004)
=(1/2)*(2/3)*(3/4)*(4/5).(2003/2004)
=1/2004
把1/3 - 1 这种写成-（ 1-1/3）然后就记下等等 ,有偶数是正数