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Three circles of equal radius r have centres at (0,0), (1,1) and (2,1). They share a common tangent line. Find the radius r.
- (sqrt(5) - 1)/2
- sqrt(5)/10
- 1/2
- (sqrt(3) - 1)/2
Correct answer: sqrt(5)/10
Solution
Requiring equal perpendicular distance r from (0,0), (1,1), (2,1) to a line, and solving the resulting system, gives the line direction and r = sqrt(5)/10.
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