(1+1/2)(1-1/2)(1+1/3)(1-1/3)...(1+1/99)(1-1/99) =3/2×1/2×4/3×2/3...100/99×98/99 =3/2×4/3×5/4×……×100/99×1/2×2/3×……×98/99 =100/2×1/99 =50/99
