$\"\"$

\

(a).

\

The function is $\"\"$ .

\

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

\

$\"\"$

\

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

\

$\"\"$

\

$\"\"$

\

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

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

Substitute $\"\"$ in the above equation

\

$\"\"$

\

$\"\"$

\

(b).

\

The function is $\"\"$ .

\

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

\

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

\

$\"\"$

\

Since $\"\"$ hence

\

$\"\"$

\

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

\

$\"\"$

\

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

\

Hence $\"\"$

\

Therefore $\"\"$

\

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

\

$\"\"$

\

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

\

$\"\"$

\

$\"\"$

\

(a). $\"\"$ .

\

(b). $\"\"$ .