The solution I am hoping to get to is at least [ 2, -1 ].
 But the fundamental solution is folow: [2C; -1C].
 You can see than Det(A)=0 and Rank(A) =1;
 Of course you are know that such systems have trivial solution [0,0].

Matrix<double> A = Matrix<double>.Build.DenseOfArray(new double[,] {
{ 1, 2 },
{ 3, 6 },
});
Vector<double> B = Vector<double>.Build.Dense(new double[] { 0, 0 });
var result = A.Solve(B); //result = Nan, Nan