共50条信息
在三角形\(ABC\)中,若\(A\)为钝角,则\(\tan B\tan C\)的值为( )
已知\(\alpha \in (\dfrac{\pi }{2},\pi )\),\(\sin \alpha =\dfrac{\sqrt{5}}{5}\).
\((1)\)求\(\sin (\dfrac{\pi }{4}+\alpha )\)的值;
\((2)\)求\(\cos (\dfrac{5\pi }{6}-2\alpha )\)的值
设\(\tan α=3\),则\( \dfrac{\sin (α-π)+\cos (π-α)}{\sin ( \dfrac{π}{2}-α)+\cos ( \dfrac{π}{2}+α)} =\) .
在\(\vartriangle ABC\)中,点\(D\)在边\(AB\)上,\(CD\bot BC,\ AC=5\sqrt{3},\ \) \(CD=5,\ \) \(BD=2AD\),则\(AD\)的长为 .
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