Question

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

Answer 1

Cosa+cosb=2cos(a+b)/2cos(a-b)/2
Cos50+cos70=2cos(50+70)/2cos(50-70)/2=2cos60cos10=2*1/2cos10=cos10
Второй тоже
Cos10+cos70=2cos40cos30=2*sqrt(3)/2cos40=sqrt(3)cos40
Sina+sinb=2sin(a+b)/2cos(a-b)/2
Sin48+sin12=2sin30cos18=2*1/2cos18=cos18

Answer 2

Sqrt=корень

Answer 3

спасибо