Tìm x biết: x^3 + 27 + (x + 3)(x – 9) = 0.
Giải thích
x3 + 27 + (x + 3)(x - 9) = 0
⇔ x3 + 33 + (x + 3)(x - 9) = 0
⇔ (x + 3)(x2 – 3x + 9) + (x + 3)(x - 9) = 0
⇔ (x + 3)(x2 – 3x + 9 + x - 9) = 0
⇔ (x + 3)( x2 – 2x) = 0
⇔ x.(x + 3).(x – 2) = 0
⇔x=0x+3=0x−2=0⇔x=0x=−3x=2
Vậy x∈0;−3;2.