Tìm x biết: x4 = 2x2 – 12x + 8.

x⁴ = 2x² – 12x + 8.

⇔ x⁴ – 2x² + 12x – 8 = 0

⇔ (x⁴ + 2x³ – 2x²) + (–2x³ – 4x² + 4x) + (4x² + 8x – 8) = 0

⇔ x²(x² + 2x – 2) – 2x(x² + 2x – 2) + 4(x² + 2x – 2) = 0

⇔ (x² + 2x – 2)(x² – 2x + 4) = 0

⇔x2+2x−2=0x2−2x+4=0
⇔x2+2x+1−3=0x2−2x+1+3=0
⇔x+12=3x−12=−3
⇔x+12=3
⇔x+1=3x+1=−3
⇔x=3−1x=−3−1

Vậy x=3−1 hoặc x=−3−1.