I've learned special relativity in school last semester, and this semester we began learning about Quantum Mechanics, and my teacher told us that there was a Relativistic Schrodinger equation.
I was under the impression that you couldn't use Quantum Mechanics and Relativity together, so why is it appropriate to have a Relativistic Schrodinger equation, and what is an example of a situation where QM and Relativity cannot be used together?