The system of linear equaltions.
$x+y+z=0$
$2x+3y+2z=5$
$2x+3y+(a^2-1)z=a+1$
(1) has infinitely many solutions for $a=4$
(2) is inconsistent when $|a|=\sqrt3$
(3) is inconsistent when $a=4$
(4) has a unique solution for $|a|=\sqrt3$
$x+y+z=0$
$2x+3y+2z=5$
$2x+3y+(a^2-1)z=a+1$
(1) has infinitely many solutions for $a=4$
(2) is inconsistent when $|a|=\sqrt3$
(3) is inconsistent when $a=4$
(4) has a unique solution for $|a|=\sqrt3$