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So Big

One side of a triangle is divided into segments of length a and b by the inscribed circle, with radius r. Prove that the area is: abr(a+b)/ab-r^2

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30-60-90 Polypuzzle

Re-arrange the pieces of the puzzle to form a rectangle and then to form an equilateral triangle. Calculate the angles and lengths.

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What is the longest stick that can be carried horizontally along a narrow corridor and around a right-angled bend?

Gold Again

Stage: 5 Challenge Level: Challenge Level:1

Why do this problem?
Use the cosine rule to find exact values for the cosines of 36 degrees and 72 degrees.

Possible approach
Introduce this problem as one of a collection of problems involving the Golden Ratio.
See Golden Trail 1 .

Key question
If you have no right angles triangles how do you introduce the cosine?