Find all values of $\displaystyle a$ such that the set $\displaystyle \{\left[ \begin {array}{c} a\\\noalign{\medskip}1\end {array} \right], \left[ \begin {array}{c} a+2\\\noalign{\medskip}a\end {array}\right]\}$ is linearly dependent.

Work for this problem:

We have $\displaystyle \left[ \begin {array}{cc} a&a+2\\\noalign{\medskip}1&a\end {array}\right]$

Row 1 - Row 2 yields:

$\displaystyle \left[ \begin {array}{cc} a&a+2\\\noalign{\medskip}a-1&2\end {array}\right]$

Now not sure where to proceed.