How to prove $ \sin x=...(1+\frac{x}{3\pi})(1+\frac{x}{2\pi})(1+\frac{x}{\pi})x(1-\frac{x}{3\pi})(1-\frac{x}{2\pi})(1-\frac{x}{\pi})...$? [duplicate]
Courtesy of Edmund Landau, from his Differential and Integral Calculus.
Courtesy of Edmund Landau, from his Differential and Integral Calculus.