[inlmath]\text{ctg}\left( \text{arcctg}\left( x-2 \right) \right)=\text{ctg}\left( \text{arcctg}\left( x-1 \right) + \text{arcctg}\left( x \right)\right)[/inlmath]
[inlmath]x-2=\frac{\text{ctg}\left( \text{arcctg}\left( x-1 \right) \right)\cdot \text{ctg}\left( \text{arcctg}\left( x \right) \right)-1}
{\text{ctg}\left( \text{arcctg}\left( x-1 \right) \right) + \text{ctg}\left( \text{arcctg}\left( x \right) \right)}[/inlmath]
[inlmath]x-2=\frac{\left( x-1 \right)x-1}{x-1+x}[/inlmath]
[inlmath]\left( x-2 \right)\left( 2x-1 \right)=x^2-x-1[/inlmath]
[inlmath]x^2-4x+3=0[/inlmath]
[inlmath]x_{1}+x_{2}=4[/inlmath]