共50条信息
已知\(\dfrac{1+\sin a}{\cos a}=- \dfrac{1}{2} \)，则\(\dfrac{\cos a}{\sin a-1} \)的值是 ( )
已知\(\sin α=- \dfrac{3}{5} \)，\(α∈\left( \dfrac{3π,2π}{2}\right) \)则\(\cos ( \dfrac{π}{4}-α) \)的值为\((\) \()\)
\(\tan \left( -\dfrac{23}{6}\pi \right)=\)
已知\(\cos\alpha{=}\dfrac{1}{3}\)，且\({-}\dfrac{\pi}{2}{ < }\alpha{ < }0\)，则\(\dfrac{\cos({-}\alpha{-}\pi)\sin(2\pi{+}\alpha)\tan(2\pi{-}\alpha)}{\sin(\dfrac{3\pi}{2}{-}\alpha)\cos(\dfrac{\pi}{2}{+}\alpha)}{=}\) ______ ．
\((2)\)已知\(\sin (\alpha -\beta )\cos \alpha -\cos (\alpha -\beta )\sin \alpha =\dfrac{3}{5}\)，\(\beta \)是第三象限角，求\(\sin (\beta +\dfrac{\pi }{4})\)的值
已知\(\sin a+\cos a= \dfrac{1}{2} \)，\(α∈(0,π)\)，则\( \dfrac{1-\tan a}{1+\tan a}= \)_________．
在\(\triangle ABC\)中，已知\(\tan \dfrac{A+B}{2}=\sin C\)，给出四个论断：\(①\tan A\cdot \cot B=1;②1 < \sin A+\sin B\leqslant \sqrt{2};③{{\sin }^{2}}A+{{\cos }^{2}}B=1\) \(;④{{\cos }^{2}}A+{{\cos }^{2}}B={{\sin }^{2}}C\)其中正确的是( )
\((1)\)已知角\(\alpha \)终边上一点\(P(m,1)\)，\(\cos \alpha =-\dfrac{1}{3}\)，求\(\tan \alpha \)的值；
\((2)\)求值：\(\dfrac{\tan 150{}^\circ \cos \left( -210{}^\circ \right)\sin \left( -420{}^\circ \right)}{\sin 1050{}^\circ \cos \left( -600{}^\circ \right)}\)
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