$5,4$ - $3$ . $| x - \dfrac{21}{10} | $ = 0
⇒ $3$ . $| x - \dfrac{21}{10} | $ = $5,4$
⇒ $| x - \dfrac{21}{10} | $ = $ \dfrac{9}{5}$
⇒\(\left[ \begin{array}{l} x - \dfrac{21}{10} = \dfrac{9}{5}\\ x - \dfrac{21}{10} = -\dfrac{9}{5}\end{array} \right.\)
⇒\(\left[ \begin{array}{l} x = \dfrac{39}{10}\\ x = \dfrac{3}{10}\end{array} \right.\)
Vậy x∈{ $\dfrac{39}{10}$;$\dfrac{3}{10}$}
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