A=1/1.2+1/2.3+1/3.4+…1/2017.2018 b)B=3/1.3+3/3.5+3/5.7+…+3/199.201

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1. a)

   `A=1/(1.2)+1/(2.3)+1/(3.4)+…1/(2017.2018)`

   `A=1-1/2+1/2-1/3+1/3-1/4+…+1/2017-1/2018`

   `A=1-1/2018`

   `A=2017/2018`

   b)

   `B=3/(1.3)+3/(3.5)+3/(5.7)+…+3/(199.201)`

   `2/3B=2/(1.3)+2/(3.5)+2/(5.7)+…+2/(199.201)`

   `2/3B=1-1/3+1/3-1/5+1/5-1/7+…+1/199-1/201`

   `2/3B=1-1/201`

   `2/3B=200/201`

   `B=300/201`

    

    

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2. Đáp án:

    

   Giải thích các bước giải:

   A=1/2+1/2-1/3+…+1/2017-1/2018=1-1/2018=2017/2018

   B=3/2.(1-1/3+1/3-1/5+…1/199-1/201)=3/2.(1-1/201)=100/67

   Hok tốt

    

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