How can I convert global rotation to local rotation for objects?

[Fly7]

Hi all, I don't know if this is the right section, but I really need to solve this problem. I've been searching for the correct formula for two days. OK, here's the picture:

The global rotation of all objects (rot_x, rot_y, rot_z): red object (0.00, 45.00, 0.00), blue object (45.00, 0.00, 90.00) and green object (30.00, 35.26, 35.26).

I need to calculate the local rotation of the objects, so the local rotation of the green object should be (0.00, 45.00, 45.00). I want to be able to rotate objects locally, not globally. Here is one formula, but I don't understand how to use it:

[   1      0       0   ]
[   0    cos(a)  sin(a)] = Rx(a)
[   0   -sin(a)  cos(a)] 

[ cos(a)   0    -sin(a)]
[   0      1       0   ] = Ry(a)
[ sin(a)   0     cos(a)]

[ cos(a) sin(a)   0    ]
[-sin(a) cos(a)   0    ] = Rz(a)
[   0      0      1    ]

[URL="http://stackoverflow.com/questions/6252223/adding-local-rotation-to-global-rotation"]source[/URL]

I hope someone can help me solve this because I'm newbie in math.

 

[Fly7]

OK, I've figured out that the global rotation is in euler angles (Z is parent, then X, then Y). Now, maybe someone can help me to convert object's local angles to euler angles. I hope that makes sense to someone.