how to define var vector?

savecancel

There are two errors in your code.

First: you define variables a,b,c , that's ok, but you use strings in the list of vector entries.

Second: a,b,c are elements of the symbolic ring and cannot be converted to elements of QQ

sage:  a,b,c=var("a,b,c");v = vector([a,b,c]);v

(a,b,c)