The function is
.
Apply derivative on each side with respect to
.
Quotient Rule of differentiation:
.



.
.
Graph the functions
and
.
.
The Zero of
corresponds to the point on the graph of the function where the tangent lines are horizontal.
.
Graph the functions
and
.
.
The Zero of
corresponds to the point on the graph of the function where the tangent lines are horizontal.