Geometric Series Sum 215B10
1. The problem is to find the sum of the infinite geometric series $$12 - 6 + 3 - \ldots$$ if it converges.
2. The formula for the sum of an infinite geometric series with first term $a$ and common ratio $r$ (where $|r| < 1$) is:
$$S = \frac{a}{1 - r}$$
3. Identify the first term $a$ and the common ratio $r$:
- First term $a = 12$
- Common ratio $r = \frac{-6}{12} = -\frac{1}{2}$
4. Check if the series converges by verifying $|r| < 1$:
$$\left| -\frac{1}{2} \right| = \frac{1}{2} < 1$$
So, the series converges.
5. Calculate the sum using the formula:
$$S = \frac{12}{1 - (-\frac{1}{2})} = \frac{12}{1 + \frac{1}{2}} = \frac{12}{\frac{3}{2}} = 12 \times \frac{2}{3} = 8$$
6. Therefore, the sum of the series is $8$.
Final answer: 8