1. **State the problem:**
We want to evaluate the integral $$\int_0^6 \frac{x^2 + 8x - 3}{x + 2} \, dx$$ and express the answer in the form $a + b \ln 2$ where $a$ and $b$ are integers.
2. **Rewrite the integrand using polynomial division:**
Divide $x^2 + 8x - 3$ by $x + 2$ to express it as $$\frac{x^2 + 8x - 3}{x + 2} = Ax + B + \frac{C}{x + 2}$$ where $A$, $B$, and $C$ are constants.
3. **Perform polynomial division:**
Divide $x^2 + 8x - 3$ by $x + 2$:
$$x^2 + 8x - 3 \div (x + 2) = x + 6 + \frac{9}{x + 2}$$
Explanation:
- $x \times (x + 2) = x^2 + 2x$
- Subtract: $(x^2 + 8x - 3) - (x^2 + 2x) = 6x - 3$
- $6 \times (x + 2) = 6x + 12$
- Subtract: $(6x - 3) - (6x + 12) = -15$
Correction: The remainder is $-15$, so the division is actually:
$$x^2 + 8x - 3 = (x + 2)(x + 6) - 15$$
So,
$$\frac{x^2 + 8x - 3}{x + 2} = x + 6 - \frac{15}{x + 2}$$
4. **Rewrite the integral:**
$$\int_0^6 \frac{x^2 + 8x - 3}{x + 2} \, dx = \int_0^6 \left(x + 6 - \frac{15}{x + 2}\right) dx$$
5. **Integrate term-by-term:**
$$\int_0^6 x \, dx = \left[\frac{x^2}{2}\right]_0^6 = \frac{36}{2} = 18$$
$$\int_0^6 6 \, dx = [6x]_0^6 = 36$$
$$\int_0^6 \frac{15}{x + 2} \, dx = 15 \int_0^6 \frac{1}{x + 2} \, dx = 15 [\ln|x + 2|]_0^6 = 15 (\ln 8 - \ln 2) = 15 \ln 4$$
6. **Combine the results:**
$$\int_0^6 \frac{x^2 + 8x - 3}{x + 2} \, dx = 18 + 36 - 15 \ln 4 = 54 - 15 \ln 4$$
7. **Express $\ln 4$ in terms of $\ln 2$:**
$$\ln 4 = \ln (2^2) = 2 \ln 2$$
So,
$$54 - 15 \ln 4 = 54 - 15 \times 2 \ln 2 = 54 - 30 \ln 2$$
8. **Final answer:**
$$\boxed{54 - 30 \ln 2}$$
where $a = 54$ and $b = -30$.
Integral Rational Cfad40
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