If the lines x + 2ay + a = 0, x + 3by + 3 = 0 and x + 4cy + c = 0 are concurrent, then a, b, c are in ……
(a) A.P.
(b) H.P.
(c) G.P.
(d) A.G.P
The correct option (b) H.P.
Explanation:
∴ 1(3bc – 4bc) – 2a(c – b) + a(4c – 3b) = 0
∴ – bc – 2ac + 2ab + 4ac – 3ab = 0
∴ 2ac – ab – bc = 0
∴ 2ac = ab + bc
∴ (2/b) = (1/a) + (1/c)
∴ a, b, c are in H.P.
