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Analytical Geometry

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Joined: 30 Jul 2011
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5 Feb 2012 18:08:10 IST
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Parabola
Mathematics

OA and OB are two mutually perpendicular chords of y^2=4ax, O being the origin. Line AB will always pass through the point


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Vishal U. Karve's Avatar

Hot goIITian

Joined: 18 Jan 2012
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5 Feb 2012 18:27:44 IST
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It will pass through the focus (a,0).

It is a property of the parabola.


Hot goIITian

Joined: 30 Jul 2011
Posts: 123
5 Feb 2012 18:42:23 IST
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The answer is (4a,0).
Vishal U. Karve's Avatar

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Joined: 18 Jan 2012
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6 Feb 2012 18:34:28 IST
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Ohh..I'm sorry i got confused between another property...

Yeah the answer is (4a,0)...

As a penalty for wrong answer, I'll write the solution here....

Let co-ordinates of A and B be (at12,2at1) and (at22,2at2).  [t1 and t2 are parameters]

They lie on the parabola, evidently.

Slope of OA=2/t1

Slope of OB=2/t2

Therefore, (2/t1)*(2/t2)=(-1)

or, t1t2=(-4)

Now equation of line joining AB is

(t1+t2)y=2(x+at1t2)     (You can derive it..)

Putting t1t2=-4,

(t1+t2)y=2(x-4a)

Therefore it always is satisfied by (4a,0).


Hot goIITian

Joined: 30 Jul 2011
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7 Feb 2012 23:39:38 IST
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Thanks a lot!

New kid on the Block

Joined: 16 Feb 2012
Posts: 4
16 Feb 2012 07:04:57 IST
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 answer is [4a,0]




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