If we put the disk in the x-y plane, then we saw that . We want to know the answer when spun around the x axis . That should be the same as . So using the parallel axis theorem, eqn. 1.61, we have that . Therefore .
. We want to know the answer when
spun around the x axis 
. That should be the same
as 
. So using the parallel axis theorem,
eqn. 1.61, we have that 
.
Therefore 
.