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'Weekly Problem 25 - 2010' printed from

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Four touching circles all have radius 1 and their centres are at the corners of a square.
What is the radius of the circle through the points of contact $X, Y, Z$ and $T$?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.



This problem is taken from the UKMT Mathematical Challenges.

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