Compute the discriminant $D(x,y)of$ the function.

$f(x,y)=x^3+y^4-6x-2y^2+5$

$(Express$ numbers $in$ exact form. Use symbolic notation and fractions where needed.$)$

$D(x,y)=$

Which $of$ these points are saddle points?

$(-\sqrt[\phantom{2}]{2},0)$

$(\sqrt[\phantom{2}]{2},0)$

$(\sqrt[\phantom{2}]{2},-1)$

$(-\sqrt[\phantom{2}]{2},1)$

$(\sqrt[\phantom{2}]{2},1)$

$(-\sqrt[\phantom{2}]{2},-1)$