Medium MCQ +4 / -1 PYQ · JEE Mains 2021

Let A(1, 4) and B(1, $-$5) be two points. Let P be a point on the circle
(x $-$ 1)2 + (y $-$ 1)2 = 1 such that (PA)2 + (PB)2 have maximum value, then the points, P, A and B lie on :

  1. A a straight line Correct answer
  2. B an ellipse
  3. C a parabola
  4. D a hyperbola

Solution

P be a point on ${(x - 1)^2} + {(y - 1)^2} = 1$<br><br>so $P(1 + \cos \theta ,1 + \sin \theta )$<br><br>A(1, 4), B(1, $-$5)<br><br>${(PA)^2} + {(PB)^2}$<br><br>$$ = {(\cos \theta )^2} + {(\sin \theta - 3)^2} + {(\cos \theta )^2} + {(\sin \theta + 6)^2}$$<br><br>$= 47 + 6\sin \theta$<br><br>It is maximum if $\sin \theta = 1$<br><br>When $\sin \theta = 1,\cos \theta = 0$<br><br>So P(1, 2), A(1, 4), B(1, $-$5)<br><br>P, A, B are collinear points.

About this question

Subject: Mathematics · Chapter: Circles · Topic: Equation of a Circle

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