$\"\"$

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The differential equation is $\"\"$ , $\"\"$ .

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$\"\"$

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$\"\"$ .

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Apply integral on each side.

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$\"\"$ .

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Apply integration power rule: $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ , where $\"\"$ .

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$\"\"$

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As the $\"\"$ value in the initial condition is negative, $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$ .

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The solution of differential equation is $\"\"$ . $\"\"$

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$\"\"$ .