Đáp án:
$a,(3x + 4)² - (3x - 1)(3x + 1) = 49 $
$⇔ 9x² + 24x + 16 - (9x² - 1) = 49 $
$⇔ 9x² + 24x + 16 - 9x² + 1 = 49 $
$⇔ 24x + 17 = 49 $
$⇔ 24x = 32 $
$⇔ x = \frac{4}{3} $
$b, x² - 4x + 4 = 9(x - 2) $
$⇔ (x - 2)² - 9(x - 2) = 0 $
$⇔ (x - 2)(x - 2 - 9) = 0 $
$⇔ (x - 2)(x - 11) = 0 $
$⇔$ \(\left[ \begin{array}{l}x-2=0\\x-11=0\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=2\\x=11\end{array} \right.\)
$c, x² - 25 = 3x - 15 $
$⇔ (x - 5)(x + 5) - 3(x - 5) = 0 $
$⇔ (x - 5)(x + 5 - 3) = 0 $
$⇔ (x - 5)(x + 2) = 0 $
$⇔$ \(\left[ \begin{array}{l}x-5=0\\x+2=0\end{array} \right.\)
$⇔$ \(\left[ \begin{array}{l}x=5\\x=-2\end{array} \right.\)
$d, (x - 1)³ + 3(x + 1)² = (x² - 2x + 4)(x + 2) $
$⇔ x³ - 3x² + 3x - 1 + 3(x² + 2x + 1) = x³ + 8$
$⇔ -3x² + 3x - 1 + 3x² + 6x + 3 = 8 $
$⇔ 9x + 2 = 8 $
$⇔ x = \frac{2}{3} $
