Вычислите:
а) cos 3π cosπ + sin3π sinπ
8 8 8 8
б) sin 10° sin70°+cos70°cos10°
Вычислите cos (α-β), если 90°<α<180°, 90°<β<180° и cos α=-0,8, sin β=0,2</p>
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