1. We are asked to evaluate the definite integral $$\int_0^1 \frac{1 + 6t}{1 + 2t} \, dt$$.
2. To solve this, we use algebraic manipulation to simplify the integrand. Notice that the numerator and denominator are linear expressions.
3. Perform polynomial division or rewrite the fraction:
$$\frac{1 + 6t}{1 + 2t} = A + \frac{B}{1 + 2t}$$
for constants $A$ and $B$.
4. Multiply both sides by $1 + 2t$:
$$1 + 6t = A(1 + 2t) + B$$
$$1 + 6t = A + 2At + B$$
5. Group terms:
$$1 + 6t = (A + B) + 2At$$
6. Equate coefficients of like terms:
For $t$: $6 = 2A \implies A = 3$
For constants: $1 = A + B = 3 + B \implies B = 1 - 3 = -2$
7. So the integrand becomes:
$$\frac{1 + 6t}{1 + 2t} = 3 - \frac{2}{1 + 2t}$$
8. Rewrite the integral:
$$\int_0^1 \frac{1 + 6t}{1 + 2t} \, dt = \int_0^1 \left(3 - \frac{2}{1 + 2t}\right) dt = \int_0^1 3 \, dt - 2 \int_0^1 \frac{1}{1 + 2t} \, dt$$
9. Integrate each term separately:
$$\int_0^1 3 \, dt = 3t \Big|_0^1 = 3(1) - 3(0) = 3$$
10. For the second integral, use substitution:
Let $u = 1 + 2t$, then $du = 2 dt$, so $dt = \frac{du}{2}$.
When $t=0$, $u=1$; when $t=1$, $u=3$.
11. Substitute:
$$\int_0^1 \frac{1}{1 + 2t} \, dt = \int_1^3 \frac{1}{u} \cdot \frac{du}{2} = \frac{1}{2} \int_1^3 \frac{1}{u} \, du = \frac{1}{2} \ln|u| \Big|_1^3 = \frac{1}{2} (\ln 3 - \ln 1) = \frac{1}{2} \ln 3$$
12. Multiply by -2:
$$-2 \times \frac{1}{2} \ln 3 = -\ln 3$$
13. Combine results:
$$3 - \ln 3$$
14. Therefore, the value of the integral is:
$$\boxed{3 - \ln 3}$$
Integral Evaluation 9Deb91
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