Помогите пожалуйста решить 29,16
Дам 40 баллов

а)cos10*cos30*cos50*cos70=cos30*cos70*(cos50*cos10)=(√3/2)cos70*(½)(cos60+cos40)=(√3/4)cos70*(½+cos40)=(√3/4)((½)cos70+cos70cos40)=(√3/4))((½)cos70+(½)(cos110+cos30))=(√3/4)((½)cos70+(½)(-cos70+(√3/2)))=(√3/4)*(√3/4)=3/16

б) sin10sin30sin50sin70=1/2sin10sin50sin70=

=1/4(cos40-cos60 )sin70=1/4(cos40-0.5)sin70=

=1/4cos40sin70-1/8sin70=1/8(sin110+sin30)-1/8sin70=

=1/8sin110+1/16-1/8sin70=1/8sin(180-70)+1/16-1/8sin70=

=1/8sin70+1/16-1/8sin70=1/16=0.0625