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\(\cos α= \dfrac{3}{5} \),\(α∈\left( \dfrac{3π}{2},2π\right) \),则\(\cos \left(α- \dfrac{π}{4}\right)= (\) \()\)
已知\(a,b,c\)分别为\(\angle A,\angle B,\angle C\)的对边,向量\(\overrightarrow{m}=(\sqrt{3},-1),\overrightarrow{n}=(\cos A,\sin A)\),若\(\overrightarrow{m}\bot \overrightarrow{n}\),则\(a\cos B+b\cos A=c\sin C\),则角\(B=\)___________
已知\(\cos \theta =-\dfrac{3}{5},\theta \in (\dfrac{\pi }{2},\pi )\),则\(\sin (\theta +\dfrac{\pi }{3})=\) .
在\({\triangle }{ABC}\)中,\(a{,}b{,}c\)分别是角\(A{,}B{,}C\)的对边,若\((b{-}\dfrac{6}{5}c)\sin B{+}c\sin C{=}a\sin A\),则\(\sin A{=}({ })\)
\(\Delta ABC\)的内角\(A\),\(B\),\(C\)的对边分别为\(a\),\(b\),\(c\),已知\(2\cos C(a\cos B+b\cos A)=c.\)
\((I)\)求\(C\);
\((II)\)若\(c=\sqrt{7},\Delta ABC\)的面积为\(\dfrac{3\sqrt{3}}{2}\),求\(\vartriangle ABC\)的周长.
\((2)\)求\(\cos \)\(\left( \left. A- \dfrac{π}{6} \right. \right)\)的值.
\(\sin 27^{{∘}}\cos 18^{{∘}}{+}\cos 27^{{∘}}\sin 18^{{∘}}\)的值为\(({ })\)
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