tính giá trị của biểu thức sau: 2/3.2/4.+2/4.2/5+2/5.2/6+2/6.2/7+2/7.2/8+2/8.2/9

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1. Cho A=2/3.2/4.+2/4.2/5+2/5.2/6+2/6.2/7+2/7.2/8+2/8.2/9

   A=2.2/3.4+2.2/4.5+…+2.2/8.9

   1/4xA=1/3.4+1/4.5+…+1/8.9

   1/4xA=1/3-1/4+1/4-1/5+…+1/8-1/9

   1/4xA=1/3-1/9

   1/4xA=2/9

   A=2/9:1/4

   A=8/9

   Vậy 2/3.2/4.+2/4.2/5+2/5.2/6+2/6.2/7+2/7.2/8+2/8.2/9=8/9

   Trả lời

2. `2/3. 2/4+2/4. 2/5+2/5. 2/6+2/6. 2/7+2/7. 2/8+2/8. 2/9`

   `=2.2/3.4+2.2/4.5+2.2/5.6+2.2/6.7+2.2/7.8+2.2/8.9`

   `=4/3.4+4/4.5+4/5.6+4/6.7+4/7.8+4/8.9`

   `=4(1/3.4+1/4.5+1/5.6+1/6.7+1/7.8+1/8.9)`

   `=4(1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9)`

   `=4(1/3-1/9)`

   `=4(3/9-1/9)`

   `=4. 2/9`

   `=8/9`

   Trả lời