the JOINT SAMPLE SPACE:
Any experimental outcome can be fully described by ( Y, 
 ), where
     Y = distance from the center of the pencil to the closest line (0 
 y 
 d / 2), and
     
 = angle of the needle from the horizontal line (0 
 
 
 
).
Since we know that the pencil was randomly thrown, this means that:
     Y is uniformly distributed: