theorem Th67: :: COMPLEX2:69

for a, b being Complex st a <> 0 & b <> 0 holds
( cos (angle (a,b)) = (Re (a .|. b)) / (|.a.| * |.b.|) & sin (angle (a,b)) = - ((Im (a .|. b)) / (|.a.| * |.b.|)) )