$\"\"$

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Find $\"\"$ in terms of $\"\"$ and $\"\"$ .

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From the figure : $\"\"$ .

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$\"\"$ .

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Differentiate the above equation with respect to $\"\"$ .

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$\"\"$

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$\"\"$

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Use chain rule to find $\"\"$ in terms of $\"\"$ and $\"\"$ .

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Apply chain rule : $\"\"$ .

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$\"\"$

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Since need to write $\"\"$ in terms of $\"\"$ and $\"\"$ , replace $\"\"$ in terms of $\"\"$ .

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$\"\"$

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Consider $\"\"$ .

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Pythagorean identity : $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in equation (1).

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$\"\"$

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$\"\"$

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$\"\"$ .