Home Maths Conic Sections Parabola The line x + 2y + 3 = 0 and its conjugate wi…
Maths Conic Sections Parabola Single Correct MCQ
Published on: August 13, 2026

The line x + 2y + 3 = 0 and its conjugate with respect to the parabola y 2 = 4x are perpendicular to each other. The equation of the conjugate line is

A
2x - y + 1 = 0
B
2x - y + 5 = 0
C
2x - y + 10 = 0
D
2x - y - 10 = 0

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Text Solution

Verified by Experts
The correct answer is:
D

If the lines l 1 x+m 1 y+n 1 =0, l 2 x+m 2 y+n 2 =0 are conjugate lines w.r.to y 2 = 4ax, then l 1 n 2 +l 2 n 1 = 2am 1 m 2 .

Let the required line is 2x- y + λ λ =0

Given line is x+2y + 3= 0

By applying above condition

2 x 3 + 1. λ λ = 2 x 1.x-1 x 2

λ λ = 10

∴ ∴ Required equation is 2x – y – 10 = 0

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