M= $\displaystyle \left[ \begin{array}{ c c } 4 & -5 \\ 6 & -9 \end{array} \right]$

A transformation $\displaystyle T:\mathbb{R}^2 \rightarrow \mathbb{R}^2$ is represented by the matrixM. There is a line through the origin for which every point on the line is mapped onto itself under $\displaystyle T$.

Find a cartesian equation of this line.