$12.28 \int_{8}^{27} \frac{d x}{\sqrt[3]{x^{2}}}$
12.28 We have

$$
\int_{8}^{27} \frac{d x}{\sqrt[3]{x^{2}}}=\int_{8}^{27} x^{-2 / 3} d x=\left.\frac{x^{1 / 3}}{1 / 3}\right|_{8} ^{27}=3\left(27^{1 / 3}-8^{1 / 3}\right)=3
$$

Answer: 3.