If A=(abcd)A = \begin{pmatrix} a & b \\ c & d \end{pmatrix}A=(acbd), what is the condition for AAA to be singular (non-invertible)?
ad−bc=0ad - bc = 0ad−bc=0
ad−bc≠0ad - bc \neq 0ad−bc=0
a+d=0a+d = 0a+d=0
a=b=c=d=0a=b=c=d=0a=b=c=d=0