Question

найдите значение выражения: sin(11pi/12)*cos(11pi/12)

Answer 1

$sin(11 \pi /12)*cos(11 \pi /12)=0,5*(2sin(11 \pi /12)*cos(11 \pi /12))=\\\\=0,5sin(2*11 \pi /12)=0,5sin(11 \pi /6)=\\\\=0,5sin(12 \pi /6-\pi /6)=0,5sin(2 \pi - \pi /6)=\\\\=-0,5sin( \pi /6)=-0,5*0,5=-0,25$