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9. Значения выражений \ Тип 5


\(\DeclareMathOperator{\tg}{tg}\)\(\DeclareMathOperator{\ctg}{ctg}\)\(\DeclareMathOperator{\arctg}{arctg}\)\(\DeclareMathOperator{\arcctg}{arcctg}\)
Найдите \(\ctg\alpha\), если \(\sin\alpha=\dfrac{4}{\sqrt{20}}\) и \(\alpha\in(0;\frac{\pi}{2})\).