$\"\"$

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The speed of blood is $\"\"$ .

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Where $\"\"$ is a constant, $\"\"$ is the radius of artery and $\"\"$ is measured in centimeters per second.

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Apply derivative on each side with respect to $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ is a constant distance $\"\"$ .

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ cm/sec.

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The rate is $\"\"$ cm/sec.

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$\"\"$

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The rate is $\"\"$ cm/sec.