看
原式=1÷2X3÷3X4÷4X5÷5X6÷6X7÷7X8÷8X9=1÷2X3÷3X4÷4X5÷5X6÷6X7÷7X8÷8X9=1÷2X(3÷3)X(4÷4)X(5÷5)X(6÷6)X(7÷7)X(8÷8)X9=1÷2X9=9/2
1÷2/3÷3/4÷4/5÷5/6÷6/7÷7/8÷8/9=1÷(2/3×3/4×4/5×5/6×6/7×7/8×8/9)=1÷2/9=9/2=4.5
4.5