Toán Lớp 10: Cho sina =1/2(0
Toán Lớp 10: Cho sina =1/2(0
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Toán Lớp 10: Cho sina =1/2(0
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0 < a < {90^0}\\
\Leftrightarrow 0 < \cos a < 1\\
Do:{\sin ^2}a + {\cos ^2}a = 1\\
\Leftrightarrow {\cos ^2}a = 1 – {\left( {\dfrac{1}{2}} \right)^2} = \dfrac{3}{4}\\
\Leftrightarrow \cos a = \dfrac{{\sqrt 3 }}{2}\\
\Leftrightarrow \tan a = \dfrac{{\sin a}}{{\cos a}} = \dfrac{{\dfrac{1}{2}}}{{\dfrac{{\sqrt 3 }}{2}}} = \dfrac{{\sqrt 3 }}{3}\\
\Leftrightarrow \cot a = \dfrac{1}{{\tan a}} = \sqrt 3 \\
Vậy\,\cos a = \dfrac{{\sqrt 3 }}{2};\tan a = \dfrac{{\sqrt 3 }}{3};\cot a = \sqrt 3
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