JEE Main 2019 Mathematics question
If a circle C passing through the point (4, 0) touches the circle externally at the point (1, −1), then the radius of C is:
Answer: (A)
Solution
Centre on the line of centres beyond (1, −1): (1 + 3r/5, −1 − 4r/5); distance to (4, 0) equals r ⇒ r = 5.