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if the lines x + 2ay + a = 0, x + 3by +...

if the lines `x + 2ay + a = 0`, `x + 3by + b = 0` and `x + 4cy + c = 0` are concurrent, then a, b, c are in: (1) A.P.(2) G.P.(3) H.P.(4) A.G.P.

A

A.P.

B

G.P.

C

H.P.

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
C
Given lines will be concurrent if
`|(1,2a,a),(1,3b,b),(1,4c,c)| = 0 implies -bc+2ac-ab = 0`
`implies b = (2ac)/(a+c) implies a,b,c` are in H.P.
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