[1/2×3]=[1/2]-[1/3];
[1/3×4]=[1/3]-[1/4];
[1/6×7]=[1/6]-[1/7];
①[1/2×3]+[1/3×4]+[1/4×5]+…+[1/9×10],
=[1/2]-[1/3]+[1/3]-[1/4]+[1/4]-[1/5]+…+[1/9]-[1/10],
=[1/2]-[1/10],
=[2/5];
②[1/1×2]+[1/2×3]+[1/3×4]+[1/4×5]+…+[1/99×100],
=[1/1]-
[1/2×3]=[1/2]-[1/3];
[1/3×4]=[1/3]-[1/4];
[1/6×7]=[1/6]-[1/7];
①[1/2×3]+[1/3×4]+[1/4×5]+…+[1/9×10],
=[1/2]-[1/3]+[1/3]-[1/4]+[1/4]-[1/5]+…+[1/9]-[1/10],
=[1/2]-[1/10],
=[2/5];
②[1/1×2]+[1/2×3]+[1/3×4]+[1/4×5]+…+[1/99×100],
=[1/1]-