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

If the locus of the mid-point of the line segment from the point (3, 2) to a point on the circle, x2 + y2 = 1 is a circle of radius r, then r is equal to :

  1. A ${1 \over 4}$
  2. B ${1 \over 2}$ Correct answer
  3. C 1
  4. D ${1 \over 3}$

Solution

Let P(h, k) and point on the circle is (cos$\theta$, sin$\theta$)<br><br>$\therefore$ ${{3 + \cos \theta } \over 2} = h$ and ${{2 + \sin \theta } \over 2} = k$<br><br>cos$\theta$ = 2h $-$ 3 and sin$\theta$ = 2h $-$ 2<br><br>Squaring and adding we get<br><br>${(2h - 3)^2} + {(2h - 2)^2} = 1$<br><br>$\Rightarrow 4{x^2} - 12x + 9 + 4{y^2} - 8y + 4 = 1$<br><br>$\Rightarrow 4{x^2} + 4{y^2} - 12x - 8y + 12 = 0$<br><br>$\Rightarrow {x^2} + {y^2} - 3x - 2y + 3 = 0$<br><br>Radius = $\sqrt {{9 \over 4} + 1 - 3} = {1 \over 2}$

About this question

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

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