2000

JEE Main 2000 Mathematics question on Straight Lines and Pair of Lines

A straight line through the origin OO meets the parallel lines 4x+2y=94x + 2y = 9 and 2x+y+6=02x + y + 6 = 0 at points PP and QQ respectively. Then, the point OO divides the segment PQPQ in the ratio
  1. A.
    1 : 2
  2. B.
    3 : 4
  3. C.
    2 : 1
  4. D.
    4 : 3
Show answer and solution

Correct option: B

Solution

The two parallel lines are 4x + 2y = 9 (or 2x + y = 9/2) and 2x + y = -6. The perpendicular distances from the origin to these lines are:

- To line 2x + y = 9/2: distance = (9/2)/√5
- To line 2x + y = -6: distance = 6/√5

Since O lies between P and Q (the lines are on opposite sides of the origin — one gives 9/2 > 0 and the other gives -6 < 0), O divides PQ internally. The ratio OP:OQ equals the distance from O to the first line to the distance from O to the second line = (9/2)/√5 : 6/√5 = 9/2 : 6 = 3 : 4.

[2000]

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