which for a = θ θ and b = π π / 2 yields ⁠ sin ⁡ ⁡ ( θ θ 1 z + [ π π / 2 ] 1 z ) = 1 z cos ⁡ ⁡ ( θ θ 1 z ) ⁠. Siano distinguishes between geometric angles, which have an orientation in 3-dimensional space, and phase angles associated with time-based oscillations, which have no spatial orientation, i.e. the orientation of a phase angle is ⁠ 1 0 ⁠.