13.
$$\mathbf { A } = \left( \begin{array} { c c }
2 & a
a - 4 & b
\end{array} \right)$$
where \(a\) and \(b\) are non-zero constants.
Given that the matrix \(\mathbf { A }\) is self-inverse,
- determine the value of \(b\) and the possible values for \(a\).
The matrix \(\mathbf { A }\) represents a linear transformation \(M\).
Using the smaller value of \(a\) from part (a), - show that the invariant points of the linear transformation \(M\) form a line, stating the equation of this line.
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