7) Упростите: $$\frac{\sin \frac{\pi}{18} \cos \frac{\pi}{9} + \sin \frac{\pi}{9} \cos \frac{\pi}{18}}{ \cos \frac{\pi}{18}} =$$

$$\frac{\sin \frac{\pi}{18} \cos \frac{\pi}{9} + \sin \frac{\pi}{9} \cos \frac{\pi}{18}}{ \cos \frac{\pi}{18}} = \frac{\sin(\frac{\pi}{18} + \frac{\pi}{9})}{\cos \frac{\pi}{18}} = \frac{\sin(\frac{\pi}{18} + \frac{2\pi}{18})}{\cos \frac{\pi}{18}} = \frac{\sin(\frac{3\pi}{18})}{\cos \frac{\pi}{18}} = \frac{\sin(\frac{\pi}{6})}{\cos \frac{\pi}{18}} = \frac{\frac{1}{2}}{\cos \frac{\pi}{18}} = \frac{1}{2\cos \frac{\pi}{18}}$$

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