How do we get the wave function of Ligand Group Orbitals with the same symmetry as that of the corresponding metal orbitals

In the book Principles of Structure and Reactivity by Huheey, Chapter 14, the author has taken linear combination of ligand orbitals to form ligand group orbitals and then further combination of LGOs(Ligand Group Orbital) with corresponding orbital of metal which has the same symmetry as that of the LGO. 


I do not understand how they calculated the wave function for the Ligand Group Orbitals.
[![An example of wave function for the ligand group orbital with the same symmetry as the a1g irreducible representation](https://i.stack.imgur.com/TATYj.png)](https://i.stack.imgur.com/TATYj.png)


