How do I use a matrix that has a variable?

Question

I seem to be getting an error whenever I try running this piece of code.

 Matrix12[n_] := {{1, 0}, {0, {\[Kappa]1[n]}/{\[Kappa]2[n]}}}

I've already defined the n dependent functions kappa1 and kappa2 but it still doesn't work. I keep getting a 'Tag list in...... is protected'. Is it that this functionality is not supported by the program itself or is my code wrong in how it's written?

Answer 1

\[Kappa]1[n_] := 2 n + 1;
\[Kappa]2[n_] := n^2 + 1;
matrix12[n_] := {{1, 0}, {0, {\[Kappa]1[n]}/{\[Kappa]2[n]}}}
matrix12[3]

gives

{{1,0},{0,{7/10}}}