$\"\"$

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The expression is $\"\"$ .

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Graph the summation expression $\"\"$ :

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$\"\"$

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Observe the graph:

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The summation value of $\"\"$ . $\"\"$

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The expression is $\"\"$ .

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$\"\"$ .

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Apply summation formula $\"\"$ .

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Apply summation formula $\"\"$ .

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In this case $\"\"$ .

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$\"\"$

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$\"\"$ . $\"\"$

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$\"\"$ .