Maths-
General
Easy

Question

The locus of the point of intersection of the tangents to the parabola x2 – 4x – 8y + 28 = 0 which are at right angle is - 

  1. y = 0    
  2. y = – 1    
  3. x = 1    
  4. y = 1    

The correct answer is: y = 1


    x2 – 4x – 8y + 28 = 0
    locus of pt of intersection of  perpendicular tangents is directrix
    x2 – 4x + 4 = 8y – 28 + 4 rightwards double arrow (x – 2)2 = 8y – 24
    (x – 2)2 = 8(y – 3) rightwards double arrow X2 = 8Y
    equation of directrix
    Y = – 2 rightwards double arrow y – 3 = – 2 rightwards double arrow y = 1

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