$\"\"$

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$\"\"$ and $\"\"$ .

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The general formula of $\"\"$ -term sum of a geometric series is $\"\"$ .

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Find $\"\"$ .

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Substitute $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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Substitute $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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Divide equation $\"\"$ by equation $\"\"$ .

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$\"\"$

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$\"\"$

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The value of $\"\"$ is $\"\"$ .

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$\"\"$

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The value of $\"\"$ is $\"\"$ .