1/(1×2×3)=(1/2[1/(1×2)－1/(2×3)]1/(2×3×4)=(1/2)[1/(2×3)－1/(3×4)]1/(3×4×5)=(1/2)[1/(3×4)－1/(4×5)]……1/(8×9×10)=(1/2)[1/(8×9)－1/(9×10)]则原式=(1/2)[1/(1×2)－1/(9×10)]=(1/2)[(1/2)－1/(90)]=11/45
