Stage: 4 Challenge Level: 
Triangle ABC is equilateral. D, the midpoint of BC, is the centre of the semi-circle whose radius is R which touches AB and AC, as well as a smaller circle with radius r which also touches AB and AC.
What is the value of r/ R?
Calculating with ratio & proportion. Tangents. Scale factors. Tessellations. Similarity. Individual. chemistry. Radius (radii) & diameters. Isosceles triangles. Enlargements.
Published July 1998.
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