Integral Interval
1. **State the problem:** We are given a continuous function $f(x)$ on the interval $[0,2]$ with two integral conditions:
$$\int_0^2 (f(x) + x) \, dx = 8$$
and
$$\int_0^1 f(x) \, dx = 2$$
We need to find the value of
$$\int_1^2 f(x) \, dx$$
2. **Recall the properties of integrals:** The integral of a sum is the sum of the integrals:
$$\int_a^b (f(x) + g(x)) \, dx = \int_a^b f(x) \, dx + \int_a^b g(x) \, dx$$
3. **Apply this to the given integral:**
$$\int_0^2 (f(x) + x) \, dx = \int_0^2 f(x) \, dx + \int_0^2 x \, dx = 8$$
4. **Calculate the integral of $x$ from 0 to 2$:**
$$\int_0^2 x \, dx = \left[ \frac{x^2}{2} \right]_0^2 = \frac{2^2}{2} - 0 = \frac{4}{2} = 2$$
5. **Substitute back:**
$$\int_0^2 f(x) \, dx + 2 = 8 \implies \int_0^2 f(x) \, dx = 6$$
6. **Use the property of integrals over adjacent intervals:**
$$\int_0^2 f(x) \, dx = \int_0^1 f(x) \, dx + \int_1^2 f(x) \, dx$$
7. **Substitute known values:**
$$6 = 2 + \int_1^2 f(x) \, dx$$
8. **Solve for the unknown integral:**
$$\int_1^2 f(x) \, dx = 6 - 2 = 4$$
**Final answer:**
$$\boxed{4}$$