Talk:Proof of Wallis product/to do

• Move the derivation of

${\frac {\sin(x)}{x}}=\left(1-{\frac {x^{2}}{\pi ^{2}}}\right)\left(1-{\frac {x^{2}}{4\pi ^{2}}}\right)\left(1-{\frac {x^{2}}{9\pi ^{2}}}\right)\cdots$

to Euler-Wallis formula.

• Make some effort to justify this derivation, possibly using the PlanetMath article on the Weierstrass factorization theorem.

• Note how to use this formula to compute

$\sum _{n=1}^{\infty }{\frac {1}{n^{2}}}.$

• A historical account would be nice.