Question

4sin 7п/12 cos 7п/12

Answer 1

Используем формулы sin2a = 2sinacosa и приведения:
$4sinfrac{7pi}{12}cosfrac{7pi}{12}=2*2sinfrac{7pi}{12}cosfrac{7pi}{12}=2sin(2*frac{7pi}{12})=2sinfrac{7pi}{6}=\=2sin(frac{6pi}{6}+frac{pi}{6})=2sin(pi+frac{pi}{6})=-2sinfrac{pi}{6}=-2*frac{1}{2}=-1.$