a) Giải PT \(\text{4 ( 5x - 3 ) - 3 ( 2x + 1 ) = 9}\)
\(\Leftrightarrow\) \(\text{20x - 12 -6x - 3 = 9}\)
\(\Leftrightarrow\) \(\text{14x = 9 + 12 + 3}\)
\(\Leftrightarrow\) \(\text{14x = 24}\)
\(\Leftrightarrow\) \(\text{x =}\dfrac{\text{24 }}{\text{14}}=\dfrac{\text{12}}{\text{7}}\)
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b) \(\text{| x – 9 | = 2x + 5}\)
+) Với \(\text{x ≥ 9}\) thì \(\text{|x – 9| = x – 9}\) ta có PT \(\text{x – 9 = 2x + 5}\) \(\Leftrightarrow\) \(\text{x = - 14}\) ( loại)
+) Với \(\text{x < 9}\) thì \(\text{|x – 9| = 9 – x}\) ta có PT \(\text{9 – x = 2x + 5}\) \(\Leftrightarrow\) \(\text{x = 4/3}\) (thỏa mãn)
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c) ĐKXĐ \(\text{x ≠ ±3}\)
\(\Leftrightarrow\) \(\text{2(x + 3) + 3(x – 3) = 3x + 5}\)
\(\Leftrightarrow\) \(\text{5x – 3 = 3x + 5}\)
\(\Leftrightarrow\) \(\text{x = 4 (thỏa mãn ĐKXĐ)}\)
