\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Find the matrix representing a reflection in the line \(y=x\).
$$ \mathbf{M} = \begin{pmatrix}\input{145095}{}{3em}{2em}{}{} & \input{245095}{}{3em}{2em}{}{}\\ \input{345095}{}{3em}{2em}{}{} & \input{445095}{}{3em}{2em}{}{}\\ \end{pmatrix}$$