This is LaTeX code:
[latex]
\frac{1}{2^n}\cot{\frac{x}{2^n}}=\frac{1}{2^n}\dfrac{\cot^2{\frac{x}{2^{n+1}}}-1}{2\cot{\frac{x}{2^{n+1}}}} =\frac{1}{2^{n+1}}\dfrac{\cot^2{\frac{x}{2^{n+1}}}-1}{\cot{\frac{x}{2^{n+1}}}}
[/latex]