cos 3π/8 cosπ/8 + sin3π/8 sinπ/8=соs(3π/8 - π/8)=cos2π/8=cosπ/4=√2/2
sin 10° sin70°+cos70°cos10°= cos(70° - 10°)=cos60° = 1/2
cos 3π/8 cosπ/8 + sin3π/8 sinπ/8=соs(3π/8 - π/8)=cos2π/8=cosπ/4=√2/2
sin 10° sin70°+cos70°cos10°= cos(70° - 10°)=cos60° = 1/2