How do I use summation notation to write the series 2.2 + 8.8?

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How do I use summation notation to write the series 2.2 + 8.8?

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Answer 1 · 2014-09-20T17:39:10

This very short series appears to be geometric, with a ratio of 4, and a first term of 2.2.

2.2 + 8.8 = 11

I would write: $S_{2} = (\frac{2.2 (1 - 4^{2})}{1 - 4}))$ $S_2=((2.2(1-4^2))/(1-4)))$
from the explicit formula $S_{n} = (\frac{a_{1} (1 - r^{n})}{1 - r})$ $S_n=((a_1(1-r^n))/(1-r))$ . In the formula, $a_{1}$ $a_1$ represents the first term, r stands for the ratio between terms, and $S_{n}$ $S_n$ means "the sum of n terms".

You can also use Sigma, or summation notation: my screenshot where i=1 indicates to start with substituting in i = 1 as the exponent of 4, and multiplying by 2.2. The 2 at the top of the Sigma indicates that one should stop summing when one substitutes in 1 = 2, which would be the second term to add.

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How do I use summation notation to write the series 2.2 + 8.8?

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