Let C1 be the circle in the third quadrant of radius 3, that touches both coordinate axes. Let C2 be the circle with centre (1, 3) that touches C1 externally at the point ( , ). If ( - )2 = mn, (m, n) = 1, then m + n is equal to
- 22
- 13
- 9
- 31
Answer
(1) 22
Solution
C1 lies in the third quadrant, touches both axes, radius 3 centre O1(-3, -3).
Centre of C2: O2(1, 3)
O1O2 = 42 + 62 = 52 = 2 13
the circles touch externally, the point of contact lies on O1O2 at distance 3 (radius of C1) from O1.
( , ) = (-3, -3) + 32 13(4, 6) = (-3 + 6 13, -3 + 9 13 )
- = 3 13 ( - )2 = 913
m = 9, n = 13 m + n = 22
Answer: (1)