ét o ét giúp mình đi

$\dfrac{x+1}{1}+\dfrac{2x+3}{3}+\dfrac{3x+5}{5}+....+\dfrac{20x+39}{39}=22+\dfrac{4}{3}+\dfrac{6}{5}+.....+\dfrac{40}{39}$ 

$⇔x+1+\dfrac{2x}{3}+1+\dfrac{3x}{5}+1+....+\dfrac{20x}{39}+1=22+\dfrac{4}{3}+\dfrac{6}{5}+.....+\dfrac{40}{39}$ 

$⇔20+x+\dfrac{2x}{3}+\dfrac{3x}{5}+....+\dfrac{20x}{39}=22+2(\dfrac{2}{3}+\dfrac{3}{5}+.....+\dfrac{20}{39})$ 

$⇔20+x(1+\dfrac{2}{3}+\dfrac{3}{5}+....+\dfrac{20}{39})=20+2(1+\dfrac{2}{3}+\dfrac{3}{5}+.....+\dfrac{20}{39})$ 

$⇔x(1+\dfrac{2}{3}+\dfrac{3}{5}+....+\dfrac{20}{39})=2(1+\dfrac{2}{3}+\dfrac{3}{5}+.....+\dfrac{20}{39})$ 

$⇔x=2$

Vậy `S={2}`