Ответ:
Пошаговое объяснение:
cos20° = cos(90° - 70°) = sin70°
sin150° = sin(90° + 60°) = -cos60°
2)
sin510° = sin(510°-360°) = sin150°
tg(-840°) = tg(-840° + 1080°) = tg(240°)
cos1000° = cos(1000° - 1080°) = cos(-80°) = cos80°
4a-(3a+(5a-4)=4a-(3a+5a- 4)=4a-(8a-4)=4a-8a+4=-4a+4
-4*2/7+4=-8/7+4=-8/7+28/7=-8+28/7=20/7=2 6/7