The question is that i shall find all numbers for a so that det (A)=0
i basicly dont know what trick i shall use!
edit: i did start to det it and set it to zero but i get wrong
Expand these and solve for a.
$\displaystyle 2\left| {\begin{array}{rr} a & 1 \\ 2 & {2a + 2} \\ \end{array} } \right| - \left| {\begin{array}{rr} { - 2} & 1 \\ {2a} & 2 \\ \end{array} } \right| + 3\left| {\begin{array}{rr} { - 2} & a \\ a & 2 \\ \end{array} } \right| = 0$