$\"\"$

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The given values $\"\"$ .

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$\"\"$ (nth term $\"\"$ of a geometric sequence formula)

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

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

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

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

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The 4th term $\"\"$ .