Question

преобразовать в сумму cos7Π/12 *cosΠ/12

Answer 1

cos$frac{7pi}{12}$*cos$frac{pi}{12}$=$frac{cos( frac{7pi}{12}+ frac{pi}{12} )+cos( frac{7pi}{12}- frac{pi}{12} )}{2}$=$frac{cos frac{8pi}{12}+cos frac{6pi}{12} }{2}$=$frac{cos frac{2pi}{3}+cos frac{pi}{2} }{2}$=$frac{-0.5+0}{2}$=-0.25