Question #224020

The perpendicular OY is drawn from the centre O of the ellipse x2/a2 + y2/b2 = 1 to any tangent. Prove that the locus of Y is (x2 + y2 )2 = a2x2 + b2 y2.


1
Expert's answer
2021-08-19T07:02:36-0400

Let p(x,y) be the foot of perpendicular to a tangent

y=mx±a2m2+b2(1)y=mx\pm \sqrt{a^2m^2+b^2}\cdots (1)\\ from Centre

slope of OY = 1m\frac{-1}{m}\\

Equation of OY is

y=1xm    m=xy(2)y=\frac{-1x}{m} \implies m=\frac{-x}{y} \cdots (2)

p(x,y) lies on tangent,

y=xy.x±a2(xy)2+b2y=xy.x±a2x2y2+b2y=xy±a2x2+b2y2y2y2+x2=±a2x2+b2y2(x2+y2)2=x2a2+b2y2.y=\frac{-x}{y}.x\pm\sqrt{a^2(\frac{-x}{y})^2+b^2}\\ y=\frac{-x}{y}.x\pm\sqrt{a^2\frac{x^2}{y^2}+b^2}\\ y=\frac{-x}{y}\pm\sqrt{\frac{a^2x^2+b^2y^2}{y^2}}\\ y^2+x^2=\pm\sqrt{a^2x^2+b^2y^2}\\ (x^2+y^2)^2=x^2a^2+b^2y^2.


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