Area Parametric
1. **State the problem:** Find the exact area of the region R bounded by the curve $C$ with parametric equations $x = 1 - \frac{1}{2}t$, $y = 2^t - 1$, the line $x = -1$, and the x-axis.
2. **Recall the parametric area formula:** The area under a parametric curve from $t=a$ to $t=b$ is given by
$$\text{Area} = \int_a^b y \frac{dx}{dt} dt$$
where $\frac{dx}{dt}$ is the derivative of $x$ with respect to $t$.
3. **Find the limits for $t$:**
- At $x=0$ (point A), solve $0 = 1 - \frac{1}{2}t$ gives $t=2$.
- At $x=-1$, solve $-1 = 1 - \frac{1}{2}t$ gives $t=4$.
So the region $R$ corresponds to $t$ from 4 to 2 (note the order).
4. **Calculate $\frac{dx}{dt}$:**
$$\frac{dx}{dt} = -\frac{1}{2}$$
5. **Set up the integral for the area:**
$$\text{Area} = \int_4^2 (2^t - 1) \left(-\frac{1}{2}\right) dt = \int_2^4 \frac{1}{2}(2^t - 1) dt$$
6. **Evaluate the integral:**
$$\int_2^4 \frac{1}{2}(2^t - 1) dt = \frac{1}{2} \int_2^4 (2^t - 1) dt = \frac{1}{2} \left( \int_2^4 2^t dt - \int_2^4 1 dt \right)$$
7. **Integrate each term:**
- $$\int 2^t dt = \frac{2^t}{\ln 2}$$
- $$\int 1 dt = t$$
So,
$$\frac{1}{2} \left[ \frac{2^t}{\ln 2} - t \right]_2^4 = \frac{1}{2} \left( \frac{2^4}{\ln 2} - 4 - \frac{2^2}{\ln 2} + 2 \right)$$
8. **Simplify the expression:**
$$= \frac{1}{2} \left( \frac{16}{\ln 2} - 4 - \frac{4}{\ln 2} + 2 \right) = \frac{1}{2} \left( \frac{12}{\ln 2} - 2 \right) = \frac{6}{\ln 2} - 1$$
**Final answer:**
$$\boxed{\frac{6}{\ln 2} - 1}$$
This is the exact area of the shaded region $R$.