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<p>&lt;=&gt; x(x - 5) - 3(x - 5) = 0</p><p>&lt;=&gt; (x - 5)(x - 3) = 0</p><p>TH1: x - 5 = 0 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;TH2: x - 3 = 0</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;x &nbsp; &nbsp; &nbsp; = 5 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;x &nbsp; &nbsp; &nbsp; = 3</p><p>Vậy x ∈ { 5; 3 }</p>