помогите
cos 2*40 / (cos 40 +sin 40) = (cos^2 40-sin^2 40)/ (cos 40 +sin 40)=
= (cos 40 +sin 40) (cos 40 -sin 40) /(cos 40 +sin 40) = cos 40-sin 40
cos80 cos^2(40)-sin^2(40) (cos40-sin40)(cos40+sin40) **********= ******************=*********************= cos40-sin40 cos40+sin40 cos40+sin40 cos40+sin40