а)
cos10*cos50*cos70 = cos10*cos50*cos(90-20) = cos10*cos50*sin20 =
cos50*(sin(20-10)+sin(20+10))/2 = cos50*(sin10+sin30)/2 = (cos50*sin10+cos50*(1/2))/2 =
((sin(10-50)+sin(10+50))/2+cos50*(1/2))/2 = (sin(-40)+sin60+cos50)/4 =
(cos50-sin40+V3/2)/4 = (cos50-sin(90-50)+V3/2)/4 = (cos50-cos50+V3/2)/4 = V3/8
б)
числитель cos64*cos4 - cos86*cos26 = cos64*cos4 - cos(90-4)*cos(90-64) =
cos64*cos4 - sin(4)*sin(64) = cos(64+4) = cos68 = cos(90-22) = sin22
знаменатель cos71*cos41 - cos49*cos19 = cos71*cos41 - cos(90-41)*cos(90-71) =
cos71*cos41 - sin41*sin71 = cos(71+41) = cos112 = cos(90+22) = -sin22
Ответ -1
(может указанные ответы не отсюда???)