( 2x + 5 )² = ( x + 2 )²
⇔ 4x² + 20x + 25 = x² + 4x + 4
⇔ 4x² + 20x + 25 - x² - 4x - 4 = 0
⇔ 3x² + 16x + 21 = 0
⇔ 3x² + 9x + 7x + 21 = 0
⇔ 3x( x + 3 ) + 7( x + 3 ) = 0
⇔ ( x + 3 )( 3x + 7 ) = 0
⇔ \(\left[ \begin{array}{l}x + 3 = 0\\3x + 7 =0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=-3\\x=$\frac{-7}{3}$ \end{array} \right.\)
Vậy : \(\left[ \begin{array}{l}x=-3\\x=$\frac{-7}{3}$ \end{array} \right.\)
~CHÚC BẠN HỌC TỐT~
