a) \(\sin {105^0} = \sin ({180^0} - {105^0}).\)
\(\Rightarrow \sin {105^0} = \sin {75^0}.\)
b) \(\cos {170^0} = - \cos ({180^0} - {170^0}). \)
\(\Rightarrow \cos {170^0} = - \cos {10^0}.\)
c) \(\eqalign{
& \cos {122^0} = - \cos ({180^0} - {122^0}). \cr
& \Rightarrow \cos {122^0} = - \cos {58^0}. \cr} \)