As eiθ=cosθ+isinθ
eπ8i=cos(π8)+isin(π8) and
eπ2i=cos(π2)+isin(π2)
and eπ8i⋅eπ2i=(cos(π8)+isin(π8))(cos(π2)+isin(π2))
= cos(π8)cos(π2)+cos(π8)×isin(π2)+isin(π8)×cos(π2)+isin(π8)×isin(π2)
= cos(π8)cos(π2)+icos(π8)sin(π2)+isin(π8)cos(π2)+i2sin(π8)sin(π2)
= cos(π8)cos(π2)+icos(π8)sin(π2)+isin(π8)cos(π2)−sin(π8)sin(π2)
= [cos(π8)cos(π2)−sin(π8)sin(π2)]+i[cos(π2)sin(π8)+sin(π2)cos(π8)]
= cos(π8+π2)+isin(π8+π2)
= eπ8+π2