# Stationary point

Introduction: Just as for the optimization of functions of one variable, for the optimization of functions of two variables the stationary points are crucial.

Definition: Let $z(x,y)$ be a function of two variables. A point $(x,y)$ such that
• $z'_x(x,y)=0$
• $z'_y(x,y)=0$
is called a stationary point of the function $z(x,y)$.