4 целых 3/8×(7/15-5/3)+2×2,8=
35/8×(-6/5)+5,6
(-7/8×6/5+5,6)-7/4×3+28/5
-21/4+28/5=7/20=0,35
Нечего не видно на фотографии -_-
Cos(a + b) * cos(a - b) = (cosa * cosb - sina * sinb) * (cosa * cosb + sina * sinb) =
= cos^2 a * cos^2 b - sin^2 a * sin^2 b = cos^2 a * (1 - sin^2 b) -
- (1 - cos^2 a) * sin^2 b = cos^2 a - cos^2 a*sin^2b - sin^2 b + cos^2 a*sin^2 b=
= cos^2 a - sin^2 b