Maths tutor here. At that age I was very inspired by Fermat's Last Theorem by Simon Singh. It's not a technical book but gave me my first idea of what mathemati

Maths tutor here. At that age I was very inspired by Fermat's Last Theorem by Simon Singh. It's not a technical book but gave me my first idea of what mathematicians actually do and how the process works. This book motivated me to major in maths. Anything by Ian Stewart would also be good, 'Letters to a Young Mathematician' springs to mind. Given that you use the word 'maths' with an s I'm guessing you're not American. If you're British like me, I would recommend avoiding American books for high schoolers because they will assume quite different prerequisites.