2 E_{10} E_{20} ⟨ \cos (φ_{1} - φ_{2}) ⟩ = 2 E_{10} E_{20} \frac{1}{Δ t} \int_{0}^{Δ t} \cos (φ_{1} - φ_{2}) d t

${2 E_{10} E_{20} \langle\cos(\varphi_1 - \varphi_2) \rangle = 2 E_{10} E_{20} \frac{1}{\Delta t}\int_0^{\Delta t} \cos(\varphi_1 - \varphi_2)dt}$

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