(x + 2)² = 9(x² - 4x + 4)
⇔ x² + 4x + 4 = 9x² - 36x + 36
⇔ x² + 4x + 4 - 9x² + 36x - 36 = 0
⇔ -8x² + 40x - 32 = 0
⇔ -8(x² - 5x + 4) = 0
⇒ x² - 5x + 4 = 0
⇔ x² - 4x - x + 4 = 0
⇔ x(x - 4) - (x - 4) = 0
⇔ (x - 4)(x - 1) = 0
⇔ \(\left[ \begin{array}{l}x-4=0\\x-1=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=4\\x=1\end{array} \right.\)
Vậy x = 4 hoặc x = 1
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4(2x + 7)² - 9(x + 3)² = 0
⇔ [2(2x + 7) - 3(x + 3)] . [2(2x + 7) + 3(x + 3)] = 0
⇔ (4x + 14 - 3x - 9) . (4x + 14 + 3x + 9) = 0
⇔ (x + 5) . (7x + 23) = 0
⇔ \(\left[ \begin{array}{l}x+5=0\\7x+23=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=-5\\x=\frac{-23}{7}\end{array} \right.\)
Vậy x = -5 hoặc x = `\frac{-23}{7}`
