Golden ratio

There are 16 NRICH Mathematical resources connected to Golden ratio
Gold Again
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Gold Again

Age
16 to 18
Challenge level
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Without using a calculator, computer or tables find the exact values of cos36cos72 and also cos36 - cos72.
Golden Thoughts
problem

Golden Thoughts

Age
14 to 16
Challenge level
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Rectangle PQRS has X and Y on the edges. Triangles PQY, YRX and XSP have equal areas. Prove X and Y divide the sides of PQRS in the golden ratio.
About Pythagorean Golden Means
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About Pythagorean Golden Means

What is the relationship between the arithmetic, geometric and harmonic means of two numbers, the sides of a right angled triangle and the Golden Ratio?