Question

вычислите. ( sin 5п/12 sin 7п/12 -cos 5п/12 cos 7п/12)

Answer 1

$-(cos \frac{5\pi}{12}cos \frac{7\pi}{12} -sin \frac{5\pi}{12} sin \frac{7\pi}{12} )\\ -(cos( \frac{5\pi}{12}+ \frac{7\pi}{12})\\ -(cos \pi) =-(-1)=1$