1) cos70° + cos50° 2) cos70° + cos10° 3) sin48° - вопрос №6508548170502701034812 от Ульяна122004 17.08.2021 14:26

Question

Алгебра: 1) cos70° + cos50° 2) cos70° + cos10° 3) sin48° + sin12°

Ульяна122004 · Answer

Cosa+cosb=2cos(a+b)/2cos(a-b)/2Cos50+cos70=2cos(50+70)/2cos(50-70)/2=2cos60cos10=2*1/2cos10=cos10Второй тожеCos10+cos70=2cos40cos30=2*sqrt(3)/2cos40=sqrt(3)cos40Sina+sinb=2sin(a+b)/2cos(a-b)/2Sin48+sin12=2sin30cos18=2*1/2cos18=cos18...