IIT JEE , AIEEE Forum - Mathematics , Analytical Geometry

visu.prakash

PQ is the double ordinate of the parabola y^2=4x .The locus of its point of trisection is

(a)9y^2=4

(b)9y^2+4=0

(c)4y^2=9

(d)4y^2+9=0

ankur.kkhurana

let the point of trisection be (h,k)

and p be (a,b)
and p be (a,c)

now in parabola double ordinates are opp. in sign but equal in magnitude.

so b= -c
now,
h= a + 2 a =a;
3
k=(b+ 2c) /3

k=c/3
c=3k

now (a,c) lie on parabola so by putting there value we get

9k² =4h

replacing h ank k by x and y
9y² =4x

it is required locus
ans. = (a)

if u found ans satisfactory plz. rate

taruntanuj007

wats double ordinate ???

khyatigupta

Double ordinate is any chord perpendicular to the axis of a parabola. hope u understood this.

taruntanuj007

thanx khyati how do we find it is there any specific equation like t= 0 t =s1 or just use logic!!!

ankurgupta91

there is no such specific equation
u hv to use the logic acc to the question

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