Again From SL Loney

Show that the perpendiculars from the centre upon all chords, which join the ends of perpendicular diameters, are of constant length in an ellipse.

3 Answers

262
Aditya Bhutra ·

using the standard eqn of ellipse -> x2/a2 +y2/b2 =1

let one the diameters be y=mx

therefore the other diameter is y =-b2a2mx

( since m1*m2 = -b2/a2)

find out their points of intersection with the ellipse.

then form the eqn of a chord and find the perp. distance.

OR you can also use parametric coordinates (acost,bsint) and (acos(90+t),bsin(90+t) )as the ends of diameters and then proceed.

1
Vatika ·

I was looking for a less tedious method to solve it. And is m1*m2 not equal to -1 as they are pendiculars.

71
Vivek @ Born this Way ·

Use the formula for chord of ellipse joining two points with eccentric angles α , α + Π/2

You'll get the equation of chord as

x/a cos(α+Π/4) + y/b sin(α+Π/4) = cos (Π/4)

Obviously, perpendicular on it from (0,0) are of constant length.,.

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