I'm neither bright nor a teenager but I have been enjoying working through Spivak's Calculus. I picked it up because it was recommended as a good intro to pure

I'm neither bright nor a teenager but I have been enjoying working through Spivak's Calculus. I picked it up because it was recommended as a good intro to pure mathematical thinking for someone who knows calculus. I've found it challenging but it has delivered on that promise. There are many good recommendations here but I do think it will be good for them to gain some exposure to pure mathematics. It's different than what's typically taught in high school so they can start to get an idea whether they actually want to be a mathematician or instead focus on applied math in an engineering discipline. Also you're probably going to get a computing bias here. I found the threads on physicsforums.com helpful so you might ask there as well if you want a different bias. (https://www.physicsforums.com/forums/science-and-math-textbooks.21/ https://www.physicsforums.com/forums/science-and-math-textbo...)