I did explain it during 18:55 to 20:55 but to be more specific for your query, for calculation of z as 1/sqrt(2). I have converted the whole circuit into admittance so that shunt stubs can be easily added. This is like a lambda/4 transformer circuit whose load admittance is 1+j and required input input admittance before left side stub is 1-j so that after adding left side admittance of j it will become 1-j+j=1. That is why I have taken square root of 1-j and 1+j for characteristic admittance of the lambda/4 line. Using this logic for the odd mode analysis too gives 1-j load admittance to be converted into 1+j for impedance matching. Hence characteristics admittance is square root of these two. Finally characteristics admittance is converted into characteristic impedance. Do remember, these values are normalised value. Hope it helps. If you still have query, let me know. Thank you.

Thanks

Yes

See the video again. It's explained clearly.