Hi, another question from me again

A transformation $\displaystyle T$ : $\displaystyle R^2 \rightarrow R^2$ is represented by the matrix $\displaystyle A = \left(\begin{array}{cc}4&4\\4&-2\end{array}\right)$.

Find:

a) The two eigen values for A

b) A cartesian equation for each of the two lines passing through the origin which are invariant under $\displaystyle T$.

a) This was easy enough, -4 and 6.

b) No idea how to start this, anyone got any pointers?

Thanks