Mitchell J. answered 04/05/21
Dartmouth grad, Current math PhD student with 7+ years experience
If we know that the dot product is 4, and the cross product has magnitude 2, we can utilize the following identities:
Therefore, if we divide the magnitude of the cross product by the dot product, which is 2/4=.5, we get the tangent of theta. To get theta itself, we simply take the inverse tangent of this ratio, which is the inverse tangent of .5, which is about .46 radians