The function is
.
Find the first partial derivative
.
.
Differentiate partially with respect to
treating
and
as constant.

.
Find the first partial derivative
.
.
Differentiate partially with respect to
treating
and
as constant.



.
Find the first partial derivative
.
.
Differentiate partially with respect to
treating
and
as constant.



.
First partial derivatives are
,
and
.