Câu hỏi 21Khai triển $\left(\frac{x}{3}-2\right)^3$.$\frac{x^3}{27}-8$$\frac{x^3}{27}-2x^2+4x-8$$\frac{x^3}{27}-\frac23x^2+2x-8$$\frac{x^3}{27}-\frac23x^2+4x-8$$\frac{x^3}{27}-6x^2+4x-8$