2.4

[serena li]

For the question asking to find the power-series expansion about the given point for the function and find the largest disc where the series are valid, I am confused about how to find the valid largest disc. Thank you so much.

[Victor Ivrii]

Either investigate the power series or to use theorem that if $f$ is analytic in some disc $D(z_0,r)$, then the expansion at its center $z_0$ converges in this disc.