(x + 2) (3 - 4x) = x² + 4x + 4

Bạn tham khảo:
$( x + 2 )( 3 - 4x ) = x² + 4x + 4$
$⇔ ( x + 2 ) ( 3-4x ) - ( x + 2)² = 0$ 
$⇔ ( x + 2 )( 3 - 4x - x - 2 ) = 0$ 
$⇔ ( x + 2 ) ( 1 - 5x ) = 0$ 
⇔ \(\left[ \begin{array}{l}x+2=0\\1-5x=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=-2\\x=\dfrac{1}{5}\end{array} \right.\)