A circle C of radius 2 lies in the second quadrant and touches both the coordinate axes. Let r be the radius of a circle that has centre at the point (2,5) and intersects the circle C at exactly two points. If the set of all possible values of r is the interval ( , ), then 3 -2 is equal to :
- 10
- 12
- 14
- 15
Answer
(4) 15
Solution
Circle C has radius 2 and touches both axes in the 2nd quadrant, so its centre is (-2,2).
[figure]
Distance between centres: d= 42+32=5
Two circles cut at exactly two points when
|r-2|<5<r+2
3<r<7 (dashed circles are the limiting tangent cases), so =3, =7
3 -2 =15
Answer: (4)