How do I calculate angles in a moving reference frame using relativity?

[dead1327]

Certain particle moving with velocity v in a sitema O; its direction forms an angle μ with the axis X. To determine the corresponding angle in the system X^´ which moves with velocity V over the system or in the positive direction of X axis if the X and X^´ match.

 

[zhermes]

What do you need help with?
What are the relevant equations?
What are the important concepts?
What have you tried so far?

 

[dead1327]

I need your help because I do not understand how to start these exercises left me doubt if they can do would be helpful