Centre square

What does Pythagoras' Theorem tell you about the radius of these circles?
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Problem

The diagram shows two identical large circles and two identical smaller circles whose centres are at the corners of a square.

The two large circles are touching, and they each touch the two smaller circles.

The radius of the small circles is $1cm$.

What is the radius of the large circles in centimetres?



 

 

Image
Centre Square


 

 

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