Two distinct chords

Geometry Level 2

If two distinct chords of a parabola y 2 y^{2} = 4 a x 4ax , passing through (a,2a) are bisected by the line x + y = 1 x+y=1 ,then length of latus rectum can be

6 2 4 5

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1 solution

Aditya Lalbondre
Apr 20, 2015

Any point on the line x+ y= 1 can betaken as(t,1-t)

Equation of chord with this as midpoint is

y(1-t) -2a(x+t) = ( 1 t ) 2 (1-t)^{2} -4at

It passes through (a,2a)

therefore, t 2 t^{2} -2t+2 a 2 a^{2} -2a+1=0

This should have two distinct real roots so

a 2 a^{2} -a<0

0<a<1

length of latus rectum < 4

So ,the answer is 2

Thnx very much

Aashwin Sharma - 2 years, 8 months ago

Y two distinct real roots?

bhumika mittal - 2 years, 8 months ago

Log in to reply

Yu can't understand . It is way beyond your imagination

Aditya Narayan - 2 years, 6 months ago

Because there are two chords no ? The intersections of these chords with the line will represent the two solutions of that equation

Chinmay K - 2 years, 1 month ago

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