Let the circles C1 : |z|=r and C2 : |z-3-4i|=5, z C, be such that C2 lies within C1. If z1 moves on C1, z2 moves on C2 and |z1-z2|=2, then |z1-z2| is equal to :
- 12
- 17
- 22
- 24
Answer
(3) 22
Solution
C2: centre (3, 4), radius 5.
Distance of its centre from O = 9+16=5, so C2 passes through O.
For z2 on C2: 0 |z2| 5+5=10
C2 lies within C1 r>10
|z1-z2| is least when z2 is the point of C2 farthest from O (at distance 10) and z1 is the point of C1 on the same ray:
|z1-z2|=r-10=2 r=12
|z1-z2| is greatest when z1 is on the opposite ray:
|z1-z2|=r+10=12+10=22
Answer: (3)