The problem is:

In the equation of the plane: Ax+By+Cz+D=0 spanned in R^3 by a=(1,3,0) and b=(0,1,2) find the parameters A,B,C and D.

I don`t have any clue about how to solve this problem. Does anybody have a good suggestion?

My second problem is:

Let "a", "b" and "c" be vectors in R^3. If "a" belongs to the plane spanned by "b" and "c", can these three vectors be linearly independent?

My answer to this would be, no they are always linearly dependent because "a" can be written in any case as a combination of "b" and "c" - is my answer correct?