Let the centre of a circle, passing through the points (0, 0), (1, 0) and touching the circle x2 + y2 = 9, be (h, k). Then for all possible values of the coordinates of the centre (h, k), 4 (h2 + k2 ) is equal to .
Answer
9
Solution
The circle passes through O(0, 0), so its radius is r = h2 + k2 (distance of the centre from O).
Since O lies inside x2 + y2 = 9 (radius 3, centre O), the circle must touch it internally:
distance between centres = 3 - r
h2 + k2 = 3 - h2 + k2 h2 + k2 = 32
4(h2 + k2) = 9 for both centres ( 12, 2 )
Answer: 9