1．（a）Write down the exact value of \(\cos 405 ^ { \circ }\)
（b）Hence，using a double angle identity for cosine，or otherwise，determine the exact value of \(\cos 101.25 ^ { \circ }\) ，giving your answer in the form $$a \sqrt { b + c \sqrt { 2 + \sqrt { 2 } } }$$ where \(a\) ，\(b\) and \(c\) are rational numbers．