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JEE Main 2021
Conic Sections
Hyperbola
Medium

Question

Let a line L 1 be tangent to the hyperbola x216y24=1{{{x^2}} \over {16}} - {{{y^2}} \over 4} = 1 and let L 2 be the line passing through the origin and perpendicular to L 1 . If the locus of the point of intersection of L 1 and L 2 is (x2+y2)2=αx2+βy2{({x^2} + {y^2})^2} = \alpha {x^2} + \beta {y^2}, then α\alpha + β\beta is equal to _____________.

Answer: 1

Solution

This problem asks us to find the locus of the point of intersection of a tangent to a hyperbola and a line passing through the origin perpendicular to that tangent. This specific type of locus is known as the pedal curve of the hyperbola with respect to the origin. We will derive this locus using the general equation of a tangent to a hyperbola in slope form.


1. Key Concept: Equation of a Tangent to a Hyperbola in Slope Form

For a standard hyperbola given by the equation x2a2y2b2=1\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1, the equation of a tangent line with slope mm is:

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