Question:
The value of $\frac{\cos 50^{\circ}}{\cos 130^{\circ}}$ is ______ .
Solution:
$\frac{\cos 50^{\circ}}{\cos 130^{\circ}}=\frac{\cos 50^{\circ}}{\cos \left(180^{\circ}-50^{\circ}\right)}$
$=\frac{\cos 50^{\circ}}{-\cos 50^{\circ}} \quad\left(\because \cos \left(180^{\circ}-\theta\right)=-\cos \theta\right)$
$=-1$
Hence $\frac{\cos 50^{\circ}}{\cos 130^{\circ}}=-1$
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