The differential function is
.
Apply derivative on each side with respect to
.

Rewrite the above equation.
\
The Power rule of derivative :
.





(a)
\Find the value of
when
.
The fucntion is
.
Substitute
in the above equation.



(b)
\Find the value of
when
.
The equation is 
Substitute
in the above equation.


.
(a)
.
(b)
.