Монгол Бодлогын Сан

Заавар: $\ctg2\alpha=\dfrac{1}{\tg2\alpha}$ болохыг ашигла.

Бодолт: $$\begin{align*} \text{Илэрх.}&=\dfrac{1-\tg2\alpha+\tg^22\alpha}{1-\ctg2\alpha+\ctg^22\alpha}=\dfrac{1-\tg2\alpha+\tg^22\alpha}{1-\dfrac{1}{\tg2\alpha}+\dfrac{1}{\tg^22\alpha}}\\ &=\dfrac{\cancel{1-\tg2\alpha+\tg^22\alpha}}{\dfrac{1}{\tg^22\alpha}\cdot\cancel{(\tg^22\alpha-\tg2\alpha+1)}}=\tg^22\alpha \end{align*}$$