>>909
1−(cosα+isinα)
={1-cosα}-isinα
=2{sin(α/2)}^2-2isin(α/2)cos(α/2)
=-2isin(α/2){isin(α/2)+cos(α/2)}
=2sin(α/2){cos(-π/2)+isin(-π/2)}{cos(α/2)+isin(α/2)}
=2sin(α/2){cos(α/2-π/2)+isin(α/2-π/2)}