Average Value Cube Root
1. **State the problem:** Find the average value of the function $f(x) = \sqrt[3]{x}$ on the interval $[1,8]$.
2. **Formula for average value of a function:** The average value $f_{avg}$ of a continuous function $f(x)$ on the interval $[a,b]$ is given by
$$f_{avg} = \frac{1}{b-a} \int_a^b f(x) \, dx$$
3. **Apply the formula:** Here, $a=1$ and $b=8$, so
$$f_{avg} = \frac{1}{8-1} \int_1^8 x^{1/3} \, dx = \frac{1}{7} \int_1^8 x^{1/3} \, dx$$
4. **Integrate the function:** Recall that
$$\int x^n \, dx = \frac{x^{n+1}}{n+1} + C$$ for $n \neq -1$.
For $n=\frac{1}{3}$,
$$\int x^{1/3} \, dx = \frac{x^{(1/3)+1}}{(1/3)+1} + C = \frac{x^{4/3}}{4/3} + C = \frac{3}{4} x^{4/3} + C$$
5. **Evaluate the definite integral:**
$$\int_1^8 x^{1/3} \, dx = \left[ \frac{3}{4} x^{4/3} \right]_1^8 = \frac{3}{4} (8^{4/3} - 1^{4/3})$$
6. **Simplify powers:**
Since $8 = 2^3$,
$$8^{4/3} = (2^3)^{4/3} = 2^{3 \times \frac{4}{3}} = 2^4 = 16$$
Also, $1^{4/3} = 1$.
7. **Calculate the integral value:**
$$\int_1^8 x^{1/3} \, dx = \frac{3}{4} (16 - 1) = \frac{3}{4} \times 15 = \frac{45}{4}$$
8. **Find the average value:**
$$f_{avg} = \frac{1}{7} \times \frac{45}{4} = \frac{45}{28}$$
**Final answer:** The average value of $f(x) = \sqrt[3]{x}$ on $[1,8]$ is
$$\boxed{\frac{45}{28}} \approx 1.607$$