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The circle passing through the intersection of the circles, x2 + y2 – 6x = 0 and x2 + y2 – 4y = 0, having its centre on the line, 2x – 3y + 12 = 0, also passes through the point :

JEE · Math · previous-year question

  1. A.(–3, 1)
  2. B.(1, –3)
  3. C.(–1, 3)
  4. D.(–3, 6)correct

Answer

D. (–3, 6)

Explanation

Let S be the circle passing through point of intersection of S1 & S2 $$ \therefore $$ S = S1 + $$\lambda $$S2 = 0 $$ \Rightarrow $$ $$S:({x^2} + {y^2} - 6x) + \lambda ({x^2} + {y^2} - 4y) = 0$$ $$ \Rightarrow $$ $$S:{x^2} + {y^2} - \left( {{6 \over {1 + \lambda }}} \right)x - \left( {{{4\lambda } \over {1 + \lambda }}} \right)y = 0$$ ....(1) Centre $$\left( {{3 \over {1 + \lambda }},{{2\lambda } \over {1 + \lambda }}} \right)$$ lies on $$2x - 3y + 12 = 0 \Rightarrow \lambda = - 3$$ put in $$(1) \Rightarrow S:{x^2} + {y^2} + 3x - 6y = 0$$ Now check options point $$( - 3,6)$$ lies on S.

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