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JEE Main 2019
Conic Sections
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Question

The line 12xcosθ+5ysinθ=6012x\cos \theta + 5y\sin \theta = 60 is tangent to which of the following curves?

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Solution

This problem asks us to identify which of the given curves is always tangent to the family of lines defined by the equation 12xcosθ+5ysinθ=6012x\cos \theta + 5y\sin \theta = 60, for any value of θ\theta. This is a classic question involving the tangency conditions for conic sections.


Key Concepts: Tangency Conditions for Conic Sections

A line given by the equation lx+my=nlx + my = n is tangent to:

  1. A circle x2+y2=r2x^2 + y^2 = r^2 if and only if r2(l2+m2)=n2r^2(l^2 + m^2) = n^2.
  2. An ellipse $\frac{x^2}{a^2} + \frac{

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