Leaving "-3²" to be "interpreted" according to context is not a good idea. Mathematical notation should be unambiguous and context-free as much as possible, not

Leaving "-3²" to be "interpreted" according to context is not a good idea. Mathematical notation should be unambiguous and context-free as much as possible, not "do what I mean". A computation involving "-3²" will be right or wrong depending on what it means; that shouldn't depend on who is reading it or under what circumstances. Not to unduly slight your teacher, but it could be they weren't sure about what "-3²" means. Everyone who teaches has gaps in their knowledge -- I sure did. :-)