(a) Use de Moivre's theorem to show that
\(\cos 5 \theta=16 \cos ^{5} \theta-20 \cos ^{3} \theta+5 \cos \theta\)
(b) Hence obtain the roots of the equation
\(32 x^{5}-40 x^{3}+10 x-\sqrt{2}=0\)
in the form \(\cos (q \pi)\), where \(q\) is a rational number.