SOS

Giải bài tìm x nhé!

Ta có: 

$\dfrac{1}{3} - \dfrac{1}{5} = \dfrac{5 - 3}{3.5} = \dfrac{2}{3.5}$ 

$\dfrac{1}{5} - \dfrac{1}{7} = \dfrac{7 - 5}{5.7} = \dfrac{2}{5.7}$

$\dfrac{1}{7} - \dfrac{1}{9} = \dfrac{9 - 7}{7.9} = \dfrac{2}{7.9}$

Do đó: 

$x + \dfrac{2}{3.5} + \dfrac{2}{5.7} + \dfrac{2}{7.9} = \dfrac{1}{2}$ 

$x + \dfrac{1}{3} - \dfrac{1}{5} + \dfrac{1}{5} - \dfrac{1}{7} + \dfrac{1}{7} - \dfrac{1}{9} = \dfrac{1}{2}$ 

$x + \dfrac{1}{3} - \dfrac{1}{9} = \dfrac{1}{2}$ 

$x + \dfrac{2}{9} = \dfrac{1}{2}$ 

$x = \dfrac{1}{2} - \dfrac{2}{9}$ 

$x = \dfrac{5}{18}$