Tìm x biết (x - 5)(x + 5) + 3(3 - x) = -11 + 10x
Giải thích
x2 – 25 + 9 − 3x + 11 − 10x = 0
⇔ x2 − 13x – 14 = 0
⇔ x2 + x − 14x – 14 = 0
⇔ x(x + 1) − 14(x + 1) = 0
⇔ (x + 1)(x − 14) = 0
⇔\(\left[ \begin{array}{l}x + 1 = 0\\x - 14 = 0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x = - 1\\x = 14\end{array} \right.\)
vậy x = –1 hoặc x = 14