$\"\"$

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The given values $\"\"$ .

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Apply alternate geometric series sum formula $\"\"$ .

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Where $\"\"$ is first term and r is common ratio.

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Product of two same signs is positive)

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$\"\"$ (Subtract denominator: $\"\"$ ) $\"\"$

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Apply multiplication property of equality: a = b then $\"\"$ .

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$\"\"$ (Multiply each side by negative 2)

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$\"\"$ (Cancel common terms)

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$\"\"$ (Multiply: $\"\"$ )

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Apply subtraction property of equality: a = b then $\"\"$ .

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$\"\"$ (Subtract 486 from each side)

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$\"\"$ (Apply additive inverse property: $\"\"$ )

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$\"\"$ (Subtract: $\"\"$ ) $\"\"$

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The value of $\"\"$ .