giải hộ mình câu này : 2/6+2/12+2/20+…=2/X.(X+1)

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giải hộ mình câu này : 2/6+2/12+2/20+…=2/X.(X+1)

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Brielle 4 tuần 2021-07-09T22:56:51+00:00 2 Answers 0 views 0

Answers ( )

    0
    2021-07-09T22:58:04+00:00

    Đáp án:

    `2/6+2/12+2/20+….+2/(x(x+1))`

    `=2(1/6+1/12+1/20+….+2/(x(x+1)))`

    `=2(1/6+1/12+1/20+….+1/(x(x+1)))`

    `=2(1/(2.3)+1/(3.4)+1/(4.5)+…+1/x-1/(x+1))`

    `=2(1/2-1/3+1/3-1/4+1/4-1/5+….+1/x-1/(x+1))`

    `=2(1/2-1/(x+1))`

    `=2((x+1-2)/(2(x+1)))`

    `=2*(x-1)/(2(x+1))`

    `=(x-1)/(x+1)`

    0
    2021-07-09T22:58:22+00:00

    `2/6+2/12+2/20+…+2/(x.(x+1))`

    `=> 2/(2.3)+2/(3.4)+2/(4.5)+…+2/(x.(x+1))`

    `=> 2 . (1/(2.3)+1/(3.4)+1/(4.5)+…+1/(x.(x+1)))`

    `=> 2 . (1/2 – 1/3 + 1/3 – 1/4 + 1/4 – 1/5 + ….+ 1/x – 1/(x+1))`

    `=> 2 . (1/2 -1/(x+1))`

    (Chúc bạn học tốt)

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