Stage: 3 Challenge Level: 
Two circles are enclosed by a rectangle 12 units by x units.
The distance between the centres of the two circles is x/3 units.
How big is x?
Area. Arcs, sectors and segments. Short problems. Mathematical reasoning & proof. Visualising. Circles. Circle theorems. Angle properties of shapes. Radius (radii) & diameters. Pythagoras' theorem.
Published March 1999.
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