tìm x (3x 7)^2- 4x^2=0
Giải thích
(3x – 7)2 – 4(x + 1)2 = 0
⇔ (3x – 7)2 – [2(x + 1)]2 = 0
⇔ (3x – 7)2 – (2x + 2)2 = 0
⇔ (3x – 7 + 2x + 2)(3x – 7 – 2x – 2) = 0
⇔ (5x – 5)(x – 9) = 0
⇔ \(\left[ \begin{array}{l}x = 1\\x = 9\end{array} \right.\)
Vậy x = 1 hoặc x = 9.