In this con figurationconfiguration as follows, we have a nice formula:
$$cos(\varphi)=\frac{OF.OE+OB.OC}{OF.OB+OE.OC}$$$$\cos(\varphi)=\frac{OF.OE+OB.OC}{OF.OB+OE.OC}$$
Is the formuaformula known? and can we generalized for higher dimentionsdimensions?