This image shows a surface known as a monkey saddle.

# Basic Description

The monkey saddle is a surface in Multivariable Calculus that belongs to the class of saddle surfaces. The surface gets its name from the fact that it has three depressions like a saddle for a monkey, which would require two depressions for the legs and one for the monkey's tail.

# A More Mathematical Explanation

Note: understanding of this explanation requires: *Calculus

### Expressions Defining the Surface

The monkey saddle is defined, in UNIQ6520a9a36fc8b2b8-balloo [...]

### Expressions Defining the Surface

The monkey saddle is defined, in Cartesian coordinates, by the equation:

$z(x,y)$$=x^2$$3 x y^2$

It can also be described by the parametric equations:

$x(u,v)=u$
$y(u,v)=v$
$z(u,v)=u^2 - 3xy^2$

The point (0,0,0) corresponds to a degenerate critical point of the function z(x,y) at (0,0). It is the surface's only stationary point, or point where the derivative of the function is zero. This point is also a saddle point, a point on the surface which is a stationary point, but not an extremum.

### Fundamental Forms

The coefficients of the first fundamental form of the monkey saddle are given by:

$E = 1 + 9(u^2 + v+2)^2$
$F = -18uv(u^2-v^2)$
$G = 1+36u^2v^2$

And the coefficients of the second fundamental form of the monkey saddle are:

$e = \frac{(6u)}{(\sqrt{1+9(u^2+v^2)^2})}$
$f = \frac{-(6v)}{(\sqrt{1+9(u^2+v^2)^2})}$
$g = \frac{-(6u)}{(\sqrt{1+9(u^2+v^2)^2})}$

#### Area Element

Thus, the area element of the monkey saddle is given by:

$dA=\sqrt{EG-F^2}du \wedge dv = \sqrt{1+9(u^2+v^2)^2}du \wedge dv$