Polar Conic Sketch A4Cfdd
1. **State the problem:** We need to sketch the graph of the conic given by the polar equation $$r = \frac{4}{4 - 2 \cos \theta}$$ and clearly label the directrices.
2. **Recall the form of the conic in polar coordinates:** The general form for a conic with focus at the pole is $$r = \frac{ed}{1 + e \cos \theta}$$ or $$r = \frac{ed}{1 - e \cos \theta}$$ where $e$ is the eccentricity and $d$ is the distance from the focus to the directrix.
3. **Rewrite the given equation:**
$$r = \frac{4}{4 - 2 \cos \theta} = \frac{4}{4(1 - \frac{1}{2} \cos \theta)} = \frac{1}{1 - \frac{1}{2} \cos \theta}$$
This matches the form $$r = \frac{ed}{1 - e \cos \theta}$$ with $$ed = 1$$ and $$e = \frac{1}{2}$$.
4. **Identify parameters:**
- Eccentricity: $$e = \frac{1}{2}$$
- Since $$ed = 1$$, then $$d = \frac{1}{e} = 2$$.
5. **Directrix location:**
- For $$r = \frac{ed}{1 - e \cos \theta}$$, the directrix is the vertical line $$x = d = 2$$.
6. **Sketching the graph:**
- The conic is an ellipse (since $$e < 1$$).
- The focus is at the pole (origin).
- The directrix is the vertical line $$x = 2$$.
- The curve is closer to the focus when $$\theta = 0$$ (since $$\cos 0 = 1$$), and farther when $$\theta = \pi$$.
7. **Plot key points:**
- At $$\theta = 0$$, $$r = \frac{4}{4 - 2(1)} = \frac{4}{2} = 2$$.
- At $$\theta = \pi$$, $$r = \frac{4}{4 - 2(-1)} = \frac{4}{6} = \frac{2}{3}$$.
8. **Label the directrix:** Draw the vertical line $$x = 2$$ on the polar plot.
**Final answer:** The sketch is an ellipse with focus at the origin, directrix at $$x=2$$, and eccentricity $$\frac{1}{2}$$. The curve is closer to the focus at $$\theta=0$$ and farther at $$\theta=\pi$$.