$\"\"$

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The function is $\"\"$ .

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The sub intervals are $\"\"$ .

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Observe the graph, width $\"\"$ .

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The right end point is $\"\"$ .

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The sum of areas of the circumscribed rectangles is called upper sum.

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Upper sum is $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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The upper sum is $\"\"$ square units.

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$\"\"$

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The left end point is $\"\"$ .

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The sum of areas of the inscribed rectangles is called lower sum.

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Lower sum is $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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The lower sum is $\"\"$ square units.

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$\"\"$

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$\"\"$ square units.

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$\"\"$ square units.