Angle between proton velocity and B-field

[Callumnc1]

Homework Statement:

Please see below

Relevant Equations:

F = qV x B

For this problem,

The solution is,

However, this may seem like a silly question, but do we need both angles?

Many thanks!

 

[kuruman]

The two angles are supplementary. Either one is correct if you only have the magnitude of the cross product.

 

[Callumnc1]

The two angles are supplementary. Either one is correct if you only have the magnitude of the cross product.

Thank you @kuruman !