Question - Suppose we have the normal's to surface z(x, y) at location A, B, C and D as shown in the corresponding locations in the figure below.
Use an xy-coordinate system such that
A is at (1, 1)
B is at (2, 1)
C is at (1, 2)
D is at (2, 2)
Compute the surface gradient for all for 4 locations. Explain.