... is¹

A bit of trigonometry: $\sin\alpha\cos\beta-\cos\alpha\sin\beta=\sin(\alpha-\beta)$, $\cos\alpha\cos\beta -\sin\alpha\sin\beta=\cos(\alpha+\beta)$, $\sin\alpha\cos\beta=[\sin(\alpha+\beta)+\sin(\alpha-\beta)]/2$

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