x(3x-1)(3x+1)(3x+2)=8 gap gap nha mn

1 bình luận về “x(3x-1)(3x+1)(3x+2)=8 gap gap nha mn”

1. x(3x-1)(3x+1)(3x+2) = 8

   ⇔ x(9x²-1)(3x+2) – 8 = 0

   ⇔ (9x³-x)(3x+2) – 8 = 0

   ⇔ 27$x^{4}$ + 18x³ – 3x² – 2x – 8 = 0

   ⇔ 27$x^{4}$ – 18x³ + 36x³ – 24x² + 21x² – 14x + 12x – 8 = 0

   ⇔ 9x³(3x-2) + 12x²(3x-2) + 7x(3x-2) + 4(3x-2) = 0

   ⇔ (9x³+12x²+7x+4)(3x-2) = 0

   ⇔ (9x³+9x²+3x²+3x+4x+4)(3x-2) = 0

   ⇔ [9x²(x+1) + 3x(x+1) + 4(x+1)](3x-2) = 0

   ⇔ (9x²+3x+4)(x+1)(3x-2) = 0 (Vì 9x²+3x+4$\neq$0)

   ⇒ \(\left[ \begin{array}{l}x+1=0\\3x-2=0\end{array} \right.\)

   ⇔ \(\left[ \begin{array}{l}x=-1\\x=\frac{2}{3}\end{array} \right.\)

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