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$\dfrac{2-x}{2002}-1=\dfrac{1-x}{2003}-\dfrac{x}{2004}$
$\dfrac{2 - x}{2002} = \dfrac{1 - x}{2003} + 1 - \dfrac{x}{2004}$
$\leftrightarrow \dfrac{2 - x}{2002} + \dfrac{2002}{2002} = \dfrac{1 - x}{2003} + \dfrac{2003}{2003} + \dfrac{2004 - x}{2004}$
$\leftrightarrow (2004 - x)(\dfrac{1}{2002} - \dfrac{1}{2003} - \dfrac{1}{2004}) = 0$
Do $\dfrac{1}{2002} - \dfrac{1}{2003} - \dfrac{1}{2004} \not= 0$ nên x = 2004