Предмет: Алгебра, автор: elvin1110

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Автор ответа: Universalka

Sin²a + Cos²a = 1
Cos²a = 1 - Sin²a = 1 - (√91/10)² = 1 - 91/100 = 9/100
Cosa = + - √(9/100) = + - 3/10 в нашем случае подходит только значение косинуса со знаком минус, так как а - угол второй четверти, а там косинус отрицательный.Значит Cosa = - 3/10
tga = Sina : Cosa = √91/10 : (- 3/10) = - √91/3
ctga = 1/tga = 1/( - √91/3) = - 3/√91

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