A= (1+1phần 1.3 )+(1+1phần 2.4)+(1+1phần 3.5)…(1+1phần 2018.2020)

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A= (1+1phần 1.3 )+(1+1phần 2.4)+(1+1phần 3.5)…(1+1phần 2018.2020)

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Eloise 3 tháng 2021-09-03T16:00:48+00:00 1 Answers 4 views 0

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    2021-09-03T16:02:46+00:00

    Đáp án:

    A = 2018 + ( 2016/2017 + 1009/2020) :2

    Giải thích các bước giải:

     A= ( 1+ 1/1.3)+ ( 1+ 1/2.4)+….+ (1+ 1/2018. 2020)

    A= (1+ 1+ 1+ 1+…+1) + ( 1/1.3+ 1/2.4+ 1/3.5 + ….+ 1/2028.2020)

    Đặt 1/1.3+ 1/2.4+ 1/3.5 + ….+ 1/2028.2020 = B

    Ta có:

    B = 1/1.3+ 1/2.4+ 1/3.5 + ….+ 1/2018.2020

    B= ( 1/1.3+ 1/3.5 +…+ 1/2017. 2019) + ( 1/2.4+ 1/4.6+…+ 1/2018.2020)

    2. B = 2. ( 1/1.3+ 1/3.5+…+ 1/2017. 2019) + 2. ( 1/2.4+ 1/4.6+…+ 1/2018.2020)

    2.B = ( 2/1.3+ 2/3.5+….+ 2/2017. 2019) + ( 2/2.4 + 2/4.6+…+ 2/2018.2020)

    2.B = ( 1- 1/3+ 1/3- 1/5+…..+ 1/2017-1/2019) + ( 1/2 – 1/4+ 1/4 – … + 1/2018 – 1/2020)

    2.B = ( 1- 1/2017) + ( 1/2- 1/2020)

    2.B = 2016/2017 + 1009/2020

    B = ( 2016/2017 + 1009/2020) : 2

    ⇒ A = 2018 + ( 2016/2017 + 1009/2020) :2

    Nhớ kiểm tra lại nhé, học tốt!

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