Prove that a matrix $M$ in $\mathcal { M } _ { 2 } ( \mathbb { R } )$ is nilpotent if and only if $\operatorname { det } ( M ) = \operatorname { tr } ( M ) = 0$.
Prove that a matrix $M$ in $\mathcal { M } _ { 2 } ( \mathbb { R } )$ is nilpotent if and only if $\operatorname { det } ( M ) = \operatorname { tr } ( M ) = 0$.