Question

помогите с 441 и 442)

Answer 1

$sin alpha cos beta pmcosalpha sin beta =sin( alpha pm beta ) \ cos alpha cos beta pmsin alpha sin beta =cos( alpha mp beta )$

$cos40cos20-sin40sin20=cos(40+20)=cos60= frac{1}{2} \ cos70cos40+sin70sin40=cos(70-40)=cos30= frac{ sqrt{3} }{2}$

$cos5xcos2x+sin5xsin2x=cos(5x-2x)=cos3x \ cos3xcos x-sin3xsin x=cos(3x+x)=cos4x \ cos beta sin5 beta -sin beta cos5 beta = sin(5 beta -beta )=sin4 beta \ sin3 alpha cos2 alpha -sin2 alpha cos3 alpha = sin(3 alpha +2 alpha )=sin2 alpha$