$\"\"$

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The expression is $\"\"$ .

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This is the sum of an arithmetic sequence $\"\"$ , with first term $\"\"$ .

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and the common difference is d = $\"\"$ 6. the nth term is $\"\"$ .

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To find the value of n.

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The nth term of an arithmetic sequence $\"\"$ .

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$\"\"$ (Substitute $\"\"$ , $\"\"$ and d = $\"\"$ 6)

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$\"\"$

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$\"\"$ $\"\"$

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$\"\"$ (Subtract 13 from each side)

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$\"\"$

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$\"\"$ (Divide each side by negative 6)

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n = 52 \ \

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The sum of the first n terms of an arithmetic sequence $\"\"$ .

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$\"\"$

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$\"\"$ $\"\"$

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The solution is $\"\"$ .