Tìm x biết: x^3 – 7x – 6 = 0
Giải thích
x3 – 7x – 6 = 0
⇔ x3 – x – 6x – 6 = 0
⇔ x(x2 – 1) – 6(x + 1) = 0
⇔ x(x – 1)(x + 1) – 6(x + 1) = 0
⇔ (x + 1)(x(x – 1) – 6) = 0
⇔ (x + 1)(x + 2)(x – 3) = 0
⇔ \(\left[ \begin{array}{l}x = - 1\\x = - 2\\x = 3\end{array} \right.\)