How useful is a second major or minor in math for an ENGINEER?

Why would it be useful? I cannot think of a reason. Go ahead and take the other interesting engineering courses. You really should be taking dynamics, it is basic knowledge, same with all your other courses (partial differential equations, design, etc.). Trading your engineering/physics education for math education does not make any sense to me. Pure math is not going to be useful, applied math will be useful but that is why we take engineering math courses so again it makes no sense to seek an auxillary degree like this. Biomed engineers going into mechatronics, I do not see how anything that a math major gets exclusively would ever be something that gives you an advantage. It only sounds good shallowly, think about it more.