(1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*......*(1+1/99)(1-1/99)
=(1+1/2)(1+1/3)...(1+1/99)(1-1/2)(1-1/3)...(1-1/99)
=[3/2*4/3...100/99]*[1/2*2/3...98/99]
=100/2*1/99
=50/99
(1+1/2)*(1-1/2)*(1+1/3)*(1-1/3)*......*(1+1/99)(1-1/99)
=(1+1/2)(1+1/3)...(1+1/99)(1-1/2)(1-1/3)...(1-1/99)
=[3/2*4/3...100/99]*[1/2*2/3...98/99]
=100/2*1/99
=50/99