$\"\"$

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The first term of the sequence is $\"\"$ .

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The recursive formula is $\"\"$ .

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Find the $\"\"$ term.

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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$\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Substitute $\"\"$ .

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$\"\"$ .

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Substitute $\"\"$ .

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$\"\"$ .

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Therefore,the fourth terms is $\"\"$ .

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$\"\"$

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The fourth terms is $\"\"$ .