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If a circle C passing through (4,0) touches the circle x^2+y^2+4 x-6 y-12=0 externally at a point (1,-1) , then the radius of the circle C is :

Options

  1. A5
  2. B2 5
  3. C4
  4. D57

Correct answer

A. 5

Step-by-step solution

Let A be the centre of given circle and B be the centre of circle C. aligned & x^2+y^2+4 x-6 y-12=0 & A=(-2,3) and B=(g, f) aligned Now, from the figure, we have -2+g 2 =1 and 3+f 2 =-1 (By mid point formula) g=4 and f=-5 Now, required radius = OB = 9+16 = 25 =5

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