MathTutoringByDrLiang said: Yes, A stands for an arbitrary 3x3 matrix. We say A>0 (A is then called positive) if every entry of A is positive, but I didn't say A has a numerical value. Furthermore, f(A) means A^6 - A^3 + 1. Click to expand... Actually \(\displaystyle f(A)=A^6 - A^3 + 1\) is an abuse of notation. If it were \(\displaystyle A^6 - A^3\) that is possible. SEE THIS How do you understand how to use \(\displaystyle +1~?\)