Question

Решите пожалуйста первый номер а и б

Answer 1

$1)quad 1-2sin^2frac{pi}{12}=(sin^2frac{pi}{12}+cos^2frac{pi}{12})-2sin^2frac{pi}{12}=cos^2frac{pi}{12}-sin^2frac{pi}{12}=\\=cos(2cdot frac{pi}{12})=cosfrac{pi}{6}=frac{sqrt3}{2}\\2)quad sinfrac{7pi}{36}cdot cosfrac{pi}{18}+cosfrac{7pi}{36}cdot sinfrac{pi}{18}=sin(frac{7pi}{36}+frac{pi}{18})=\\=sinfrac{9pi}{36}=sinfrac{pi}{4}=frac{sqrt2}{2}\\\Formylu:quad 1-2sin^2 alpha =cos2 alpha \\sin alpha cdot cos beta +cos alpha cdot sinbeta =sin(alpha +beta$