$\"\"$

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The arithmetic series is $\"\"$ .

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The first term is $\"\"$ .

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The common difference is $\"\"$ .

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Find the $\"\"$ partial sum.

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Formula for sum of arithmetic series is $\"\"$ .

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$ partial sum is $\"\"$ .

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$\"\"$

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$\"\"$ .