Tìm x, biết: (4x – 1)^2 – (x + 7)^2 = 0.
Tìm x, biết: (4x – 1)2 – (x + 7)2 = 0.
Lời giải
(4x – 1)2 – (x + 7)2 = 0
⇔ (4x – 1 – x – 7)(4x – 1 + x + 7) = 0
⇔ (3x – 8)(5x + 6) = 0
\( \Leftrightarrow \left[ \begin{array}{l}3x - 8 = 0\\5x + 6 = 0\end{array} \right.\)
\( \Leftrightarrow \left[ \begin{array}{l}x = \frac{8}{3}\\x = - \frac{6}{5}\end{array} \right.\)
Vậy \(x \in \left\{ {\frac{8}{3}; - \frac{6}{5}} \right\}\).