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.
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)\\y=mx±a2m2+b2⋯(1) from Centre
slope of OY = −1m\frac{-1}{m}\\m−1
Equation of OY is
y=−1xm ⟹ m=−xy⋯(2)y=\frac{-1x}{m} \implies m=\frac{-x}{y} \cdots (2)y=m−1x⟹m=y−x⋯(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.y=y−x.x±a2(y−x)2+b2y=y−x.x±a2y2x2+b2y=y−x±y2a2x2+b2y2y2+x2=±a2x2+b2y2(x2+y2)2=x2a2+b2y2.
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