How to determine whether a function is convex

for example x’Ax / x’Bx A and B are Positive semidefinite matrix。

Study Convex Optimization – Boyd and Vandenberghe

Per Why isn't CVX accepting my model? READ THIS FIRST! you should be telling us, not asking us, whether a function id convex.

(x'*A*x)/(x'*B*x) where A and B` are positive semidefinite, is neither convex nor concave.

Thank you very much for answering this question. I have also proved this conclusion.