Bạn tham khảo:
$\dfrac{2-x}{2002}- 1 = \dfrac{1-x}{2003} - \dfrac{x}{2004}$
$⇔ \dfrac{2-x}{2002}-1 + 2 = \dfrac{1-x}{2003} - \dfrac{x}{2004} +2$
$⇔ \dfrac{2-x}{2002}+ 1 = \dfrac{1-x}{2003} - \dfrac{x}{2004} + 2$
$⇔ (\dfrac{2-x}{2002}+ 1) =( \dfrac{1-x}{2003} +1)+ (\dfrac{-x}{2004} +1 )$
$⇔ \dfrac{2004-x}{2002} - \dfrac{2004-x}{2003} - \dfrac{2004 - x}{2004} = 0$
$⇔ ( 2004 - x ) ( \dfrac{1}{2002} - \dfrac{1}{2003} - \dfrac{1}{2004} )= 0$
$⇔ 2004 - x = 0$
$⇔ x = 2004$
Vậy PT trên có 1 nghiệm là $S =$ { $2004$ }
