# data[].attributes.body
Try to represent two variable functions, using the following interactive illustration.

# data[].attributes.attachment_link.readable_text
Normal Line - shows a line perpendicular to the surface

Tangent Plane - shows a plane that is tangent to the surface. Any line in this plane through will also be tangent to the surface.

Tangent Line (x=xA) - shows a line in a constant plane that is tangent to the surface. The plane is also shown lightly.

Tangent Line (y=yA) - shows a line in a constant plane that is tangent to the surface

Gradient Vector - shows the gradient vector which is in an plane and points in the direction of increasing function value

Contour Line - shows a contour curve where the function value is constant

Moving the view around is a good way to see the three dimensional features. Try viewing the the gradient and contour line from directly above the surface. Notice the angle between the vector and the curve. Equations for all of the items are shown when the box is checked.

# data[].attributes.attachment_link.description
Normal Line - shows a line perpendicular to the surface Tangent Plane - shows a plane that is tangent to the surface. Any line in this plane through will also be tangent to the surface. Tangent Line (x=xA) - shows a line in a constant plane that is tangent to the surface.

# data[].attributes.body
Definition of two variable function: look at the following video

# data[].attributes.attachment_link.title
Multivariable functions | Multivariable calculus | Khan Academy

# data[].attributes.body
Here you find a worksheet with three domain to be calculated. You have one hour time to complete them, so please send your work to the teacher at the end of the time available

# data[].attributes.body
To  go on with the next topic you have to look at the following padlet, named multivariable inequalities.
After that, you can look at the video of step six.

# data[].attributes.body
Domain

# data[].attributes.attachment_link.title
Ex 1: Determine the Domain of a Function of Two Variables

# data[].attributes.body
Another worksheet

# data[].attributes.body
Let's practice whit the following worksheet

# data[].attributes.body
look at the attached file

# data[].attributes.body
3D geometry

Look at the following video

# data[].attributes.attachment_link.title
Algebra 11 - Cartesian Coordinates in Three Dimensions