Stage: 5 Challenge Level: 
Why do this problem?
A simple trig. calculation involving cot and tan.
Key question
How many squares in each ring? So what are the angles?
Can you find any right angled triangles?
Stage 5 needs dealing with. Similarity. Quadratic equations. Index notation/Indices. Tangent. Long problems. Symmetry. Pythagoras' theorem. Circles. Graph sketching.
Published October 1999.
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