$\"\"$

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The equation is $\"\"$ .

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Apply partial derivative on each side with respect to x.

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$\"\"$

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$\"\"$

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$\"\"$

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The equation is $\"\"$ .

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Apply partial derivative on each side with respect to y .

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$\"\"$

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$\"\"$

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$\"\"$

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The first partial derivatives are $\"\"$ and $\"\"$