What is the extreme f(x,y)=ln(xy-1) ?

The extreme f(x,y)=ln(xy-1) is Saddle(0,0)

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extreme f(x,y)=ln(xy-1)

extreme

Saddle (0, 0)

Solution steps

Find the critical points:

(0, 0)

\frac{\partial ^{2} f}{\partial x ^{2}} = - \frac{x ^{2}}{( x y - 1 ) ^{2}}

D (x, y) = \frac{x y + 1}{( - 1 + x y ) ^{3}}

Check the sign of at each critical point

Check critical point

(0, 0) :

Saddle

Saddle (0, 0)

What is the extreme f(x,y)=ln(xy-1) ?
The extreme f(x,y)=ln(xy-1) is Saddle(0,0)