Ответ:

[tex]1) \frac{1}{2} \\ 2) \sqrt{3} [/tex]

Объяснение:

[tex]1) \cos( \frac{8\pi}{3} ) \times \cos( \frac{7\pi}{3} ) + \sin( \frac{8\pi}{3} ) \times \sin( \frac{7\pi}{3} ) [/tex]

[tex] \cos( \alpha - \beta ) = \cos( \alpha ) \times \cos( \beta ) + \sin( \alpha ) \times \sin( \beta ) [/tex]

[tex] \cos( \frac{8\pi}{3} - \frac{7\pi}{3} ) = \cos( \frac{\pi}{3} ) = \frac{1}{2} [/tex]

2) ( tg73° - tg13° ) / ( 1 + tg73° × tg13° )

tg (a-b) = ( tga - tgb ) / ( 1 + tga × tgb )

tg (73° - 13°) = tg60° = √3