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

Toán Lớp 7: Tìm /x/ biết $\frac{1}{1.3}$ + $\frac{1}{3.5}$ +…+ $\frac{1}{47.49}$ = $\frac{1}{x}$

Home/ Toán Lớp 7: Tìm /x/ biết $\frac{1}{1.3}$ + $\frac{1}{3.5}$ +…+ $\frac{1}{47.49}$ = $\frac{1}{x}$

Toán Lớp 7: Tìm /x/ biết $\frac{1}{1.3}$ + $\frac{1}{3.5}$ +…+ $\frac{1}{47.49}$ = $\frac{1}{x}$

Tháng Bảy 19, 2022 Toán học 2 Comments 0 views

Toán Lớp 7: Tìm /x/ biết
$\frac{1}{1.3}$ + $\frac{1}{3.5}$ +…+ $\frac{1}{47.49}$ = $\frac{1}{x}$

Comments ( 2 )

  1. hongocha12
    hongocha12
    19 Tháng Bảy, 2022 at 6:45 sáng
    Reply
    1/1.3 + 1/3.5 +…+ 1/47.49 = 1/x
    => 2/1.3 + 2/3.5 +…+ 2/47.49 = 2/x
    => 1 – 1/3 + 1/3 – 1/5 + …. + 1/47 – 1/49 = 2x
    => 1 – 1/49 = 2/x
    => 48/49 = 2/x
    => 48x = 49 x 2
    => 48x = 98
    => x = 49/24
     

  2. huyenmi76
    huyenmi76
    19 Tháng Bảy, 2022 at 6:45 sáng
    Reply
    1/{1.3} + 1/{3.5} + … + 1/{47.49} = 1/|x|
    $\Rightarrow$ 2/2 . (1/{1.3} + 1/{3.5} + … + 1/{47.49}) = 1/|x|
    $\Rightarrow$ 1/2 . (2/{1.3} + 2/{3.5} + … + 2/{47.49}) = 1/|x|
    $\Rightarrow$ 1/2 . (1 – 1/3 + 1/3 – 1/5 + … + 1/47 – 1/49) = 1/|x|
    $\Rightarrow$ 1/2 . (1 – 1/49) = 1/|x|
    $\Rightarrow$ 1/2 . 48/49 = 1/|x|
    $\Rightarrow$ 24/49 = 1/|x|
    $\Rightarrow$ 24 . |x| = 1 . 49
    $\Rightarrow$ 24 . |x| = 49
    $\Rightarrow$ |x| = 49 : 24
    $\Rightarrow$ $\left[\begin{matrix} |x|=\dfrac{49}{24}\\ |x|=\dfrac{-49}{24}\end{matrix}\right.$
    $\text{Vậy}$ x = 49/24 ; x = -49/24

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

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