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

Toán Lớp 7: B=$\frac{1}{9.10}$ – $\frac{1}{8.9}$ – $\frac{1}{7.8}$ = $\frac{1}{2.3}$ – $\frac{1}{1.2}$ lm hộ ạ

Tháng Chín 18, 2022 Toán học 2 Comments 0 views

Toán Lớp 7: B=$\frac{1}{9.10}$ – $\frac{1}{8.9}$ – $\frac{1}{7.8}$ -….- $\frac{1}{2.3}$ – $\frac{1}{1.2}$
lm hộ ạ

Comments ( 2 )

  1. ankim
    ankim
    18 Tháng Chín, 2022 at 9:25 chiều
    Reply
    B = 1/( 9 . 10 ) – 1/( 8 . 9 ) – 1/( 7 . 8 ) – …. – 1/( 2 . 3 ) – 1/( 1 . 2 )
    B = 1/( 9 . 10 ) – ( 1/( 8 . 9 ) + 1/( 7 . 8 ) + …. + 1/( 2 . 3 ) + 1/( 1 . 2 ) )
    B = 1/90 – ( 1/( 1 . 2 ) + 1/( 2 . 3 ) + …. + 1/( 7 . 8 ) + 1/( 8 . 9 ) )
    B = 1/90 – ( 1/1 – 1/2 + 1/2 – 1/3 + …. + 1/7 – 1/8 + 1/8 – 1/9 )
    B = 1/90 – ( 1 – 1/9 )
    B = 1/90 – 8/9 = 1/90 – 80/90
    B = ( – 79 )/90
    Vậy , B = ( – 79 )/90 .

  2. thanoanghha
    thanoanghha
    18 Tháng Chín, 2022 at 9:24 chiều
    Reply
    $\textit{Giải đáp + Lời giải và giải thích chi tiết:}$
    $\text{$\dfrac{1}{9.10}$ – $\dfrac{1}{8.9}$ -…- $\dfrac{1}{2.3}$ – $\dfrac{1}{1.2}$}$
    $\text{= $\dfrac{1}{9}$ – $\dfrac{1}{10}$ – ($\dfrac{1}{1.2}$ + $\dfrac{1}{2.3}$ +…+ $\dfrac{1}{8.9}$}$
    $\text{= $\dfrac{1}{90}$ – (1 – $\dfrac{1}{2}$ + $\dfrac{1}{2}$ -…- $\dfrac{1}{8}$}$
    $\text{= $\dfrac{1}{90}$ – (1 – $\dfrac{1}{9}$}$
    $\text{= $\dfrac{1}{90}$ – $\dfrac{8}{9}$}$
    $\text{= $\dfrac{1}{90}$ – $\dfrac{80}{90}$}$
    $\text{= $\dfrac{-79}{90}$}$
     

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

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