### Splitting a matrix

Dear SAGE community,
I am looking for a way that can help me split this matrix, A
A = matrix([[x], [x - 2*y]]), which is a linear combination of variables x, and y

into a Coefficient matrix, C = matrix([[1, 0], [1, -2]]) times the vector containing independent variables b = matrix([[x], ~~[y]]).~~

[y]]).
Basically, A = C*b
If there's a way to obtain the matrix C, would be really helpful.

-TIA