Which of the following functions is decreasing on $\left(0,\frac{\mathrm{\pi }}{2}\right)?$

$$\begin{gathered} \mathrm{In} \mathrm{the} \mathrm{interval} \left(0,\frac{\mathrm{\pi }}{2}\right) \\ \mathrm{Consider}, \mathrm{f}\left(\mathrm{x}\right)=\cos \mathrm{x}\Rightarrow \mathrm{f}\text{'}\left(\mathrm{x}\right)=-\sin \mathrm{x} \\ \mathrm{which} \mathrm{gives} \mathrm{f}\text{'}\left(\mathrm{x}\right)<0 \mathrm{in} \left(0,\frac{\mathrm{\pi }}{2}\right) \\ \mathrm{Hence}, \mathrm{f}\left(\mathrm{x}\right)= \cos \mathrm{x} \mathrm{is} \mathrm{decreasing} \mathrm{in} \left(0,\frac{\mathrm{\pi }}{2}\right) \end{gathered}$$