Answered
Since 5.0.189 you can use x,y,z in vector expressions
Circle:
(x,y)^2=1
Sphere:
(x,y,z)^2=1
Line:
v=(1,2)
A=(3,7)
v*(x,y)=v*A
The following synataxes work with GeoGebra 5.0.161:
Let list = {1,2,3,4,5}, matrix={{1,2},{3,4}}
Then
list(1) returns the first element of the list, ie 1
list(2) returns the second element of the list, ie 2
..
list(-1) returns the last element, ie 5
list(-5) returns the first one.
list(0) is undefined, as well as list(k) for k>5 or k <-5
matrix(1,1) returns the first element of the first row, ie 1
matrix(2,2), matrix(-1,2), matrix(2,-1) and matrix(-1,-1) all return the second element in second row
The same question 
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