Okay I have been racking my brain with this one for over a week and still have no clue how to do this.I need to study this for a test I am having and can't seem to figure this out
Consider an arbitrary 3D vector: A=Axx+Ayy+Azz
a) Determine the direction cosines for this vector. These are cos[], cos[] and cos [], where  is the angle between A and x , where  is the angle between A and y, and  is the angle of A and z.
b) Show that the direction cosines obey the relationship (cos[])2+(cos[])2+(cos [])2.
Solution gives all mathematical steps.