Let for any three distinct consecutive terms \( a, b, c \) of an A.P. the lines \( ax + by + c = 0 \) be concurrent at the point \( P \) and \( Q \equiv (\alpha,\beta) \) be a point such that the system of equations
\( x + y + z = 6 \)
\( 2x + 5y + \alpha z = \beta \) and
\( x + 2y + 3z = 4 \), has infinitely many solutions. The \( (PQ)^2 \) is equal to ________.