4. (a) You are given that the matrix \(\left( \begin{array} { c c } 2 & 1
- 1 & 0 \end{array} \right)\) represents a transformation \(T\).
You are given that the line with equation \(y = k x\) is invariant under T. Determine the value of \(k\).
(b) Determine whether the line with equation \(y = k x\) in part above is a line of invariant points under T.
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