If the three lines $x - 3 y = p , a x + 2 y = q$ and $a x + y = r$ form a right-angled triangle then : (1) $a ^ { 2 } - 9 a + 18 = 0$ (2) $a ^ { 2 } - 6 a - 12 = 0$ (3) $a ^ { 2 } - 6 a - 18 = 0$ (4) $a ^ { 2 } - 9 a + 12 = 0$
If the three lines $x - 3 y = p , a x + 2 y = q$ and $a x + y = r$ form a right-angled triangle then :\\
(1) $a ^ { 2 } - 9 a + 18 = 0$\\
(2) $a ^ { 2 } - 6 a - 12 = 0$\\
(3) $a ^ { 2 } - 6 a - 18 = 0$\\
(4) $a ^ { 2 } - 9 a + 12 = 0$