Jordan's Inequality

$\begin{figure}\begin{center}\BoxedEPSF{JordansInequality.epsf}\end{center}\end{figure}$

For $0\leq x\leq \pi/2,$

$\begin{displaymath} {2\over\pi}x \leq\sin x\leq x. \end{displaymath}$

References

Yuefeng, F. ``Jordan's Inequality.'' Math. Mag. 69, 126, 1996.