For the system {x+2y−z=32x+4y−2z=ax−y+2z=1\begin{cases} x + 2y - z = 3 \\ 2x + 4y - 2z = a \\ x - y + 2z = 1 \end{cases}⎩⎨⎧x+2y−z=32x+4y−2z=ax−y+2z=1 to have infinitely many solutions, what must aaa equal?
a=3a = 3a=3
a=6a = 6a=6
a=9a = 9a=9
a=1a = 1a=1