Engineering
Mathematics
Orthogonality of two Circles
Question

A circle S passes through the point (0, 1) and is orthogonal to the circles (x – 1)2 + y2 = 16 and x2 + y2 = 1.  Then

radius of S is 8

centre of S is (– 7, 1)

radius of S is 7

centre of S is (– 8, 1)

JEE Advance
College PredictorLive

Know your College Admission Chances Based on your Rank/Percentile, Category and Home State.

Get your JEE Main Personalised Report with Top Predicted Colleges in JoSA

Solution

x2 + y2 + 2gx + 2fy + c = 0 is required circle

⇒   2g1g2 + 2f1f2 = c1 + c2

       0 + 0 = c + (–1)       ⇒      c = 1          .....(1)

and       x2 + y2 – 2x – 15 = 0

             2 (–1) g + 0 = 1 + (–15)

            – 2g = – 14

            g = 7                                             .....(2)

         x2 + y2 + 14x + 2fy + 1 = 0 satisfies (0, 1)

              0 + 1 + 0 + 2f + 1 = 0       ⇒      f = – 1

          Circle is  x2 + y2 + 14x – 2y + 1 = 0

        Centre: (–7, 1)

 r=49+11=7

         option (B), (C)