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AP EAMCET · Maths · Pair of Lines

The transformed equation of \(3 x^2-4 x y=r^2\) when the coordinate axes are rotated about the origin through an angle of \(\operatorname{Tan}^{-1}(2)\) in positive direction is

  1. A \(x^2-4 y^2=r^2\)
  2. B \(2 x y+r^2=0\)
  3. C \(4 y^2-x^2=r^2\)
  4. D \(x y=r^2\)
Verified Solution

Answer & Solution

Correct Answer

(C) \(4 y^2-x^2=r^2\)

Step-by-step Solution

Detailed explanation

\(\operatorname{Tan}\theta = 2 \implies \sin\theta = \frac{2}{\sqrt{5}}, \cos\theta = \frac{1}{\sqrt{5}}\) \(x = x' \cos\theta - y' \sin\theta = \frac{x' - 2y'}{\sqrt{5}}\) \(y = x' \sin\theta + y' \cos\theta = \frac{2x' + y'}{\sqrt{5}}\)…