[再寄小读者之数学篇](2014-11-19 $\tan x/x$ 在 $(0,\pi/2)$ 上递增)

$$\bex \frac{\tan x}{x}\nearrow. \eex$$ Ref. [Proof Without Words: Monotonicity of $\tan x/x$ on $(0,\pi/2)$, The College Mathematics Journal].