Tìm x biết 5x^3 - 20x = 0
Tìm x biết 5x3 – 20x = 0.
5x3 – 20x = 0
⇔ x(5x2 – 20) = 0
⇔ 5x(x2 – 4) = 0
⇔ 5x(x – 2)(x + 2) = 0
⇔ \(\left[ \begin{array}{l}x = 0\\x = 2\\x = - 2\end{array} \right.\)
Vậy x ∈ {–2; 0; 2}.