# How do we find the inverse of a function $f(m,n)$ if there is a constant k?

I know I need to use the inverse matrice, but the problem is (the parameter) $k$, because it's a variable that can take any value depending on $k$, but it's not a variable. Think of the derivative $f'(n)(x)$, where $n$ is not a variable. I have no clue on what to do exactly.

$$f_k(m,n)^T=(m-kn,n)^T=\begin{pmatrix}1&-k\\0&1\end{pmatrix}\begin{pmatrix}m\\n\end{pmatrix}$$

What is $f_k^{-1}$?

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For some basic information about writing math at this site see e.g. here, here, here and here. – Julian Kuelshammer Oct 25 '12 at 22:25
wait k doesn't matter right? – Gladstone Asder Oct 25 '12 at 22:26
I just have to find the inverse matrice, right? – Gladstone Asder Oct 25 '12 at 22:27
your matrix (in the picture) is false, it should be $\begin{pmatrix}1&-k\\0&1\end{pmatrix}$ to coincide with the line before – Julian Kuelshammer Oct 25 '12 at 22:30
What formula of the inverse matrix do you know? – Julian Kuelshammer Oct 25 '12 at 22:31