For what value(s) of aaa does det(a55a)=0\det\begin{pmatrix} a & 5 \\ 5 & a \end{pmatrix} = 0det(a55a)=0?
a=0a = 0a=0
a=5a = 5a=5
a=±5a = \pm 5a=±5
a=−5a = -5a=−5