One way of looking at the Vieta product
is as the infinite product of a series of successive 'approximations' to 2, defined by
Now, the sequence of infinite radicals a0=1 , ai+1=1+ai√ converges exponentially to the golden ratio ϕ , and so the same sort of infinite product can be formed:
and an equivalent proof of convergence goes through. The question is, what's the value of Φ ? The usual proof of Vieta's product by way of the double-angle formula for sin doesn't translate over, and from what I know of the logistic map it seems immensely unlikely that there's any function conjugate to the iteration map here in the same way that the trig functions are suitably conjugate to the version in the Vieta product. Is there any other approach that's likely to work, or is Φ just unlikely to have any formula more explicit than its infinite product?