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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 7: 1/3+1/6+1/10+1/15+-.+1/x(2x+1)=1/10(x thuộc N*)

Tháng Tám 11, 2022 Toán học 1 Comment 0 views

Toán Lớp 7: 1/3+1/6+1/10+1/15+…..+1/x(2x+1)=1/10(x thuộc N*)

Comments ( 1 )

  1. kimnguenoanh
    kimnguenoanh
    11 Tháng Tám, 2022 at 1:54 sáng
    Reply
    Giải đáp:
    $x=\dfrac{11}{18}$
    Lời giải và giải thích chi tiết:
    $\dfrac13+\dfrac16+\dfrac{1}{10}+\dfrac{1}{15}\ +\,.\!.\!.+\ \dfrac{1}{x.(2x+1)}=\dfrac{1}{10}\\\Rightarrow\dfrac16+\dfrac{1}{12}+\dfrac{1}{20}+\dfrac{1}{30}\ +\,.\!.\!.+\ \dfrac1{2x.(2x+1)}=\dfrac{1}{20}\\\Rightarrow \dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+\dfrac{1}{5.6}\ +\,.\!.\!.+\ \dfrac{1}{2x.(2x+1)}=\dfrac{1}{20}\\\Rightarrow \dfrac12-\dfrac13+\dfrac13-\dfrac14+\dfrac14-\dfrac15+\dfrac15-\dfrac16\ +\,.\!.\!.+\ \dfrac{1}{2x}-\dfrac{1}{2x+1}=\dfrac{1}{20}\\\Rightarrow \dfrac12-\dfrac1{2x+1}=\dfrac1{20}\\\Rightarrow \dfrac1{2x+1}=\dfrac{9}{20}\\\Rightarrow 2x+1=\dfrac{20}{9}\\\Rightarrow 2x=\dfrac{11}{9}\\\Rightarrow x=\dfrac{11}{18}$

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222-9+11+12:2*14+14 = ? ( )

Nguyệt Minh

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