cos40*sin 70*cos 80 вычислить без таблиц

cos40*sin70*cos80=cos40*sin70=(1/2)*(sin (70-40)+sin (70+40)=(1/2)*(sin30+sin (90+20)=(1/2)*(1/2+cos20)=1/4+(1/2) cos20 cos40*sin70*cos80=(1/4+(1/2) cos20)*cos80=(1/4) cos80+(1/2)*(1/2) (cos (80-20)+cos (80+20)=(1/4) cos80+(1/4) (cos60+cos (90+10)=(1/4) cos80+(1/4) (1/2-sin10)=(1/4) cos (90-10)+(1/4)*(1/2) — (1/4) sin10=(1/4) sin10+1/8- (1/4sin10=1/8=0,125