Đáp án:
$\text{ (x+3)(x² -3x+9) -x(x-1) = 27 }$
$\text{⇔ (x³ +3³) - x² +x=27 }$
$\text{⇔ x³ + 27 -x² +x = 27 }$
$\text{⇔ x³ -x² +x = 27-27 }$
$\text{⇔ x³ -x² + x = 0 }$
$\text{⇔ x(x²-x+1) = 0 }$
$\text{⇔ x = 0 }$
$\text{hoặc (x²-x+1) = 0 }$
$\text{⇔ (x² -2x$\dfrac{1}{2}$ + $\dfrac{1}{4}$ + $\dfrac{3}{4}$ =0 }$
$\text{⇔ (x- $\dfrac{1}{2}$)² ≥ 0 }$
$\text{mà (x-$\dfrac{1}{2}$)² + $\dfrac{3}{4}$ > 0 }$
$\text{⇒ (x-$\dfrac{1}{2}$)² + $\dfrac{3}{4}$ vô nghiệm }$
$\text{Vậy x = 0 }$
