Evaluate the function provided by the infinite product at an argument of pi/3.

$\left(x\to\prod _{n=1}^{\infty } \left(1-\frac{4 x^2}{\pi ^2 (2 n-1)^2}\right)\right)\left(\frac{\pi }{3}\right)$

Amplification: $\left(x\to\prod _{n=1}^{\infty } \left(1-\frac{4 x^2}{\pi ^2 (2 n-1)^2}\right)\right)$ is a nameless function of $x$ , to which an argument of $\left(\frac{\pi }{3}\right)$ is given. Part of the problem is determining what that function actually is.