120/80=1,5 или 1 час 30 мин
18,47+1,30=20,17
1) 1 - sin^2 x = cos^2 x
2) 1 - cos^2 x = sin^2 x
3) <span>sin^2 3x+cos^2 3x - 1 = (<span>sin^2 3x+cos^2 3x) - 1 = 1 - 1 = 0</span></span>