`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`
