1．（a）Show that \(\sqrt { \frac { 1 + x } { 1 - x } }\) can be written in the form \(\frac { 1 + x } { \sqrt { 1 - x ^ { 2 } } }\) for \(| x | < 1\)
（b）Hence，or otherwise，find the expansion，in ascending powers of \(x\) up to and including the term in \(x ^ { 5 }\) ，of \(\sqrt { \frac { 1 + x } { 1 - x } }\)