$\"\"$

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(a).

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The function is $\"\"$ .

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

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$\"\"$

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Derivative of hyperbolic functions : $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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

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$\"\"$

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$\"\"$

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$\"\"$

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Substitute $\"\"$ in the above equation.

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$\"\"$

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$\"\"$

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(b).

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The function is $\"\"$ .

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And $\"\"$ , $\"\"$ and $\"\"$ .

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Substittute $\"\"$ in $\"\"$ .

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$\"\"$

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Since $\"\"$ hence

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$\"\"$

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Substitue $\"\"$ in $\"\"$ and equate $\"\"$ .

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$\"\"$

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Since $\"\"$ and $\"\"$ .

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Hence $\"\"$

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Therefore $\"\"$

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

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$\"\"$

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Susbtitute $\"\"$ and $\"\"$ and $\"\"$ in $\"\"$ .

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$\"\"$

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$\"\"$

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(a). $\"\"$ .

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(b). $\"\"$ .