Suppose $(1,1)$ is a critical point of a function $f$ with continuous second derivatives. What can you say about $f?$

$f_{}(1,1)=4,f_{xv}(1,1)=1,f_m(1,1)=2$

$D(1,1)=$

$$

nature of critical point: $($type max, min, or saddle$)$