Вычислите ; sin70cos65-sin25cos20

Question

Вычислите ;
sin70cos65-sin25cos20

Answer 1

Sin70°= cos (90°-70°)=cos 20°
cos 65°=sin (90°-65°)=sin25°

sin70°cos65°-sin25°cos20°=cos20°sin25° -sin25°cos20°=0