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NTA Abhyas JEE Main2020MathematicsCirclePractice

If x = 3 is the chord of contact of the circle x 2 + y 2 = 81 , then the equation of the corresponding pair of tangents, is

Options

  1. Ax 2 - 8 y 2 + 5 4 x + 7 2 9 = 0
  2. Bx 2 - 8 y 2 - 5 4 x + 7 2 9 = 0
  3. Cx 2 - 8 y 2 - 5 4 x - 7 2 9 = 0
  4. Dx 2 - 8 y 2 = 7 2 9

Correct answer

B. x 2 - 8 y 2 - 5 4 x + 7 2 9 = 0

Step-by-step solution

Put x = 3 in the equation of circle to get the point of contact, y = ± 6 2 Hence, equation of the pair of tangents is 3 x + 6 2 y - 8 1 3 x - 6 2 y - 8 1 = 0 x - 2 7 2 - 8 y 2 = 0 x 2 - 5 4 x - 8 y 2 + 7 2 9 = 0

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