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# URGENT I need help please:)

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I need help with this. Please also include a detailed explanation this topic is really new to me and I don't understand it to its fullest, and I think an explanation could help. Thank you so much!<3

Let $$S$$ be the set of all real numbers of the form

$$\frac{a_1}{3} + \frac{a_2}{3^2} + \frac{a_3}{3^3} + \dotsb$$
where $$a_i$$ is equal to either $$1$$ or $$-1$$ for each $$i$$

(a) Is the number $$\frac{1}{4}$$ in the set $$S$$

(b) Is the number $$\frac{1}{7}$$ in the set $$S$$

Thank you so much for your help!

Jun 9, 2023

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(a) No, 1/4 is not in the set S.

The number 1/4 can be represented as a geometric series with first term 1/4 and common ratio -1/3. However, the terms of the geometric series in the set S are all either 1/3 or -1/3. Therefore, 1/4 cannot be represented as a sum of terms in the set S.

(b) Yes, 1/7 is in the set S.

The number 1/7 can be represented as a geometric series with first term 1/7 and common ratio -1/3. The terms of the geometric series in the set S are all either 1/3 or -1/3. Therefore, 1/7 can be represented as a sum of terms in the set S.

Jun 9, 2023