This is called an eigenvector problem. If you search on wikipedia or
something you'll find some solutions. I haven't done these for a while,
but I think usually they don't give you the 3...
AX = 3X,
then
AX - 3X = 0
(A-3I)X = 0
I is the identity matrix, which is 3*3 in dimensions. Now you can work
out the matrix A-3I.
3I =
[3, 0, 0
0,3,0
0,0,3 ]
So, calculate A-3I. Now you just have the type of problem which is BX =
0. Solve that in the normal way to find the vector X.
