Question Number 28609 by abdo imad last updated on 27/Jan/18
$${calculate}\:{cotanx}\:−\mathrm{2}{cotan}\left(\mathrm{2}{x}\right){then}\:{simlify} \\ $$$$\sum_{{k}=\mathrm{0}} ^{{n}} \:\:\frac{\mathrm{1}}{\mathrm{2}^{{k}} }{tan}\left(\frac{\alpha}{\mathrm{2}^{{k}} }\right). \\ $$$$ \\ $$