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Express the decimal x = 0.142857142857142857… as the quotient of two integers

Let

    \[ x = 0.142857142857142857\ldots. \]

Express x as an infinite series, find the sum, and express x as a quotient of two integers.


We have

    \begin{align*}  x = 0.142857142857142857\ldots && \implies && x &= \sum_{k=1}^{\infty} \frac{142857}{1000000^k} \\[9pt]  &&&&&= 142857 \cdot \sum_{k=0}^{\infty} \left( \frac{1}{1000000} \right)^k - 142857 \\[9pt]  &&&&&= 142857 \left( \frac{1}{1-\frac{1}{1000000}} \right) - 142857 \\[9pt]  &&&&&= \frac{142857}{999999} = \frac{1}{7}. \end{align*}

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