$\,sen\frac{\,\pi\,}{5}\,\centerdot\, sen\frac{\,\pi\,}{3}\centerdot\,sen\frac{\,3\pi\,}{5}\centerdot\,sen\frac{\,5\pi\,}{3}\,$

$\,(1\,-\,sen\,x)(1\,+\,sen\,x),\phantom{X}x\,\in\,{\rm I\!R}\,$

$\,sen\,111^o\;-\;sen\,110^o$