Lagrangian about rolling disk on a horizontal plane

[BREAD]

Homework Statement

Homework Equations

The Attempt at a Solution

This is the problem in Goldstein's classical mechanics exercise 1.11
I wonder why the solution doesn't consider rotational kinetic energy (1/2 I w^2)
So, L= T = 1/2mx^2 + 1/2 I w^2 .

 

[JoePhysics]

This problem was discussed here.