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I have been looking up the golden ratio and found most of what I needed on mathworld.

The site states that [tex]\phi \ = \ \frac{1}{2}(1+\sqrt{5})[/tex].

I can see how (despite the fact that I don't understand how the ratio:

[tex]\phi \ = \ \frac{AC}{BC} \ = \ \frac{AB}{AC}[/tex] is formed but that is another matter).

The problem I am having is turing this into either

[tex]\phi \ = \ 2 cos (\frac{\pi}{5})[/tex] or [tex]\phi \ = \ \frac{1}{2} sec (\frac{2 \pi}{5})[/tex].

Can anyone give me some hints please?

Cheers.

The Bob (2004 ©)