k = (j|k| & -j|k|) = ±jk(φ) ↔ cos(φ) = (ejφ + e-jφ) / 2.
Но "k" = a + b * = [j|a| + j|b| &
-j|a| + j|b| &
-j|b| + j|a| &
-j|a| + (-j|b|)] = ±j(φ) ↔ (e+jφ/2 & e-jφ/2) = cos(φ/2).
Понеже {[a = ±ja(φ)] & [b = ±jb(φ)]} ↔ a + b = ±j [a(φ) ? b(φ)] = "k".
----------
* a + b + ...